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PRACTICAL CHEMISTRY FOR ENGINEERING STUDENTS

PEACTICAL CHEMISTEY

FOR ENGINEERING STUDENTS

ARTHUR J HALE, B.Sc.(London)

lEOTUKEKAHD BEMONSTRATOKIN OHEMISTKY ATTHECITYANDGUILDS

TECHNICAL COLLEQE, FINSBUBY

with an inteoduotoey note by

Professor R MELDOLA, D.Sc, LL.D., F.R.S

NEWYORK, BOMBAY, AND CALCUTTA

1912

AU rights reserved

L

U

INTRODUCTORY NOTE

One of the practical difficulties encountered by the teacher

incarryingoutmodernschemesof technical education arisesfrom the failure on the part of the students preparing forsome particular profession or industry to realise the impor-tance of subjects which they regard as being outside theirownprovince This difficulty isexperienced very generally

itconstantly arises,forexample, in connectionwith the fessionaltrainingofsuchclasses ofstudentsasthose preparing

pro-for medicine or pharmacy, or for the various branches of

engineering It is to this last group of students that thepresentlittlework by Mr ArthurJ.Haleespecially appeals.Those who are responsible for laying down the broad prin-ciples of training for the mechanical engineer have wiselyincluded Chemistry as"an essential subject Theleaders of

the engineering profession both in this countryand abroadareunanimous in urging the importance for engineers of a

soundknowledgeofat leastthegeneralrudimentsofchemical

science Such knowledge can only be acquired during the

earlyyearsof training,and it naturally falls to the dutyof

the chemicalstaff in our Technical Schools and Colleges to

carryoutthis partofthestudents' curriculum

Thesuccessfulteachingofa sciencewhich,likeChemistry,

ofanypractical utility in his subsequent career, and which

therefore arousesnointerestunlesshehas a special aptitude

for it, is by no means an easy task in view of the short

amount oftimewhich can beallottedto thesubject inatwo

or three years' programme crowded with other collateral

vi INTKODUCTORY NOTE

subjects The degree of success obtainable is of course

mainly dependentuponthe personality ofthe teacher— uponhis being himself sufficiently acquainted with the require-ments ofthe engineertoenablehimtotake acomprehensiveviewofthemany pointsofcontactbetweenthetwo subjects,andso to raisethe enthusiasmof the student to at leastthe

point of recognising that Chemistry has a distinct bearinguponhis profession

Itisunnecessaryto put forward anyspecial plea here on

behalf ofChemistry as a subject essential for engineers; its

general recognition and its inclusion in the curriculum is

present laboratorymanual tothe large numberof works onpractical Chemistry already in existence There is, how-ever, oneaspect of the question of the chemical training of

engineers which is apt to be overlooked, and the presentopportunity seems a fitting one for calling attention tothegreatneedin this countryofa recognised schoolof chemical

engineering In all branches of chemical industry usefulproducts are manufactured ona largescale, andthe chemicalengineer is an essential member of the staflF. Chemical

engineering is a quite specialised subject, and little or no

provision has been madefor it in our Technical Schools or

Colleges The engineering education is for the most part

mechanical or electrical; but a mechanical or electrical

engineering student with a good knowledge of Chemistry

is a chemical engineer in the making —he should be more

capable of specialising in a neglectedfield, and should thus

be able to give himself better scope for development in a

branch of his profession which is not already overcrowded

The young engineer with a sound knowledge of Chemistry

isthe veryman topassonfor specialisation into any school

of chemical engineering that may be called into existence.From the samepoint of view the importance of giving some

training to chemical students in the elementary principles

INTRODUCTOEY NOTE vii

of mechanical engineering has long been recognised in thehigher Technical Schools hereand abroad Theseconsidera-

tions will, it is hoped, lead to an enhanced appreciation ofChemistryasa subjectforengineeringstudents

Theextenttowhichtheschemeofpracticalworklaiddown

by Mr.Hale can be carriedout will obviously depend upon

theamountoftimethatthe student canspendin thetory, as distinguished from thetime he spends in attending

labora-lectures The treatment of the subject in the lecture-room

is necessarily more theoretical and descriptive, and thepresentwork, whichis essentially for laboratoryuse, should,under proper guidance from the teacher, be found to be avaluable adjunct to the systematic courses of lectures andtutorial classes which the student is expected to attendduring his first and second years

The programme of practical exercises contained in this

funda-mentallynewprinciple; its distinctive feature is the ingof the subjectwith a bias towards the use of materials

teach-familiar inconstructive industry—abiasbecoming more and more pronounced as the student progresses, and leading

science inTechnical Schools with a bias towards particularindustries, appearsto metobe educationally sound, provided

specialisation is not introduced at too early a stage Thefundamentalprinciplesof chemicalsciencecan be developed

as philosophically from the study of what may be called

" engineering"materialsasfromthosemadefamiliarthrough

the multitudes of existing text-books,and chosen becauseof

student so as to bring out the desired general principles

Itcancertainly be claimed as a matter of experience thatsuch treatment is much more successful in arousing the

interest and fixing the attention of the student

The great danger that the teacher of Chemistry to

viii INTRODUCTORY NOTE

engineering students has to encounter is the narrow view

held by some engineers concerning the function of thatscience in relation to their profession The teacher mustnever losesight ofthe educationalasdistinguished from the

technical valueof his subject—of its discipline as a mentalequipment quite irrespective of immediate utility. The

engineer who narrows his perspective of Chemistry to the

analysis of a fuel or of boiler water or flue gas, &c., is

virtually asking the teacher to provide him with a man

comparable with a workshop apprentice who has acquired

manual dexterity in some particular kind of work, but who

isdevoid of all knowledge of the scientific principles which

underlie the constructionanduse ofmachinery The modern

teacher of Chemistry will unhesitatingly declare that the

technique of analysis is in and by itself of nospecial

educa-tionalvalue Quite ordinary or even inferior students canbecome skilful in such routine work without having anyspecialaptitudeeither asengineersorchemists Theengineer-ing profession surely looks for recruits from the ranks of

students of wider calibre and whose qualifications are not

narrowlycircumscribedby manualskillonly Forthe

train-ingof suchmenthe presentlittlemanual,rightlyused,should

be foundusefulbothbyteachersandstudents

It is customary for engineering students in our technicalschoolsand colleges, to devote a short periodof timetothestudy ofchemistry

Obviously, such a course is pursued, in order that thestudent may obtain some knowledge regarding the chemi-

cal nature of the materials with which he is particularly

concerned

Such knowledge should be quantitative where possible,and students should be encouraged to analyse those sub-

stanceswhichareofprime importancetothe engineer

Ifhedoes not,subsequently,duringhisprofessional career,conduct the analytical examinationof substances which fall

in the category of Engineering Chemistry, he will find it

advantageous to understand, in some degree, the work of

the chemistwithwhom heconsults

In the following scheme, most of the experiments are

quantitative,andwhile inculcating a knowledge of the

ele-mentaryprinciples of chemistry, lead directly,and with the

least delay, totheanalysis ofwater,fuel, furnacegases, iron,

Meldola foradvice and encouragemeiltwhich hehas received

during the preparationof thiswork Heisalso indebtedto

Professor Coker, of themechanical engineering department,for friendly criticism,and to Mr F W. Streatfeild, F.I.C.,

Senior Demonstrator,formanyuseful suggestions i

Use has been made of many excellent illustrations from

various works of reference, which render the preparation

of new figures unnecessary, and for the use of which dueacknowledgmentismade

A J. H.

FiNSBUST TechnicalCollege,

London,1912.

Measurement of Volume—Measuring Vessels. Chemical

and Desiccation—The Bunsen Burner—Blowpipe Flame

—

BendingandSealing ofGlassTube—MakingIgnitionTubes

—CorkBoring—Wash-Bottle—CuttingGlassTube—Platinum

GlassTubeofWideBore—Collection ofGases—Kipp's

—

EstimationofMoisture—StopperedWeighingBottle pp.1-21

PHYSICAL CHANGE AND CHEMICAL CHANGE—PHYSICAL MIXTURES

AND CHEMICAL COMPOUNDS

Water on Sugar—Effect of HeatonSugarandMagnesium

—

Mixing Iron Filings and Sulphur—Estimation of Ironand

Sulphur in a Mixture—Effect of HeatonaMixtureof Iron

andSulphur—Properties ofSulphideof Iron pp.22-25

xii CONTENTS

COMPOSITION OF AIR AND WATER —OXIDATION AND EBDUOTION

Mag-nesiumonBurning—Burning PhosphorusinaClosedVolume

of Air—Burning Copperin Airand Examinationofthe

a ClosedVolumeof Air—PassingSteamoverRed-hotPassingHydrogenoverHeatedOxideofCopper—Preparation

Iron-of Hydrogen—Determination of Boiling Point of Water

—

Preparation of Oxygen from Mercuric Oxide—Reducing

Action of Carbon pp.26-37

OXIDES AND HYDROXIDES—BASES, ACIDS, AND SALTS

—Preparation of Copper Sulphate—Action of Acids and

DETERMINATION OF CHEMICAL EQUIVALENTS

EquivalentofaMetalbyTreatmentwithAcids—EquivalentofaMetal by Conversion to Oxide—Equivalent of a Metal byDisplacement—EquivalentofaMetalbyElectrolysis pp.46-50

SULPHIDES—COMPOUNDS OF THE ELEMENTS WITH SULPHURSulphur—Preparation of Hydrogen Sulphide—Properties of

Hydrogen Sulphide—Preparationof Barium Sulphide—

Lead from Lead Sulphide—Preparation of Mercury fromMercurySulphide pp.51-55

CONTENTS xiii

CHLORlifci AND ITS COMPOUNDS

Preparation of Hydrochloric Acid—Properties of Hydrochloric

Acid—Preparation of Sodium Bisulphate—Preparation of

ChlorineGas—Preparationof Bleaching Powder—Actionof

Peroxides on HCl—Preparation of Metallic Chlorides—

CABBON DIOXIDE, CARBONATES, AND CARBIDES

Preparationof Carbon Dioxide—Eifect of Heat onMarble

(Cal-ciumCarbonate)—Solubility of COginPotash—Solubility of

CO2 in Lime Water—Hardness of Water—Distillation of

Water—Preparation of Washing Soda—Formation of COg

duringCombustionandRespiration—VolumeofCO3Evolved

fromCaCOa—Weightof COg EvolvedfromCaCOj—

CarbonMonoxide pp.63-76

CARBON AND CARBONACEOUS SUBSTANCES

Pre-paration of Ammonia Gas Goal Analysis: Estimation of

AshinCoal—Estimationof MoistureinCoal—Estimationof

Bones—ManufactureofProducer-Gas—Preparationof

Water-Gas—Estimationof Carbon Monoxide inWater-Gas

Petro-leum: Fractional Distillation of Petroleum—Flash-PointDetermination Lubricating Oils : Examinationof—Determi-nation of Viscosity—Mineraland Vegetable Oils in Lubri-

MineralOils inTurpentine pp.77-90

SULPHITES AND SULPHATES, NITRITES AND NITRATES

CHLORATES J

Burning Sulphurin Air—Preparationof Sulphur Trioxide—

—Action of Acids on Sulphites—NitricAcidfrom Saltpetre

—Tests for Nitric Acid and Nitrates—Action of Heat on

Oxygen from Potassium Chlorate—Estimation of

MINERAL SUBSTANCES USED AS PIGMENTS

PhosphoricAcid—Phosphates—CalciumPhosphatefromBone

—

Arsenic—Marsh's Test—White Arsenic—Silica—Silicates

—

Glass—Mortars and Cements—Chromium—Potassium

Chro-mate—ChromiumOxide—Tungsten—TungsticOxide—

Man-ganese—Pyrolusite. Pigments: White Iiead—ZincWhite

SIMPLE QUALITATIVE ANALYSIS

General Principles Testsforthe Metals :Lead—Silver—osum—Tungsten

Merour-—

Merouricum—Bismuth—Copper—Cadmium

—

Alu-minium—Chromium

—

III (A). Cobalt—Nickel—Zinc—Manganese

CONTENTS XV

—Nitrous—Nitric—Hydrochloric—Phosphoric—Silicic

—

Pre-liminaryTests for Bases—PreliminaryTests for Acids—

Pre-paration of a Solution to Test for Bases—Preparation ofa

Substance—Table to be Used when Testing for Bases in

VOLtTMBTEIC ANALYSIS

StandardSolutions—Normal—Semi-normal—Centi-normal—

droxide—To FindtheStrengthof PotashSolution—To Find

the StrengthofAmmoniaSolution—ToFindtheStrengthof

HydrochloricAcidSolution—EstimationofCopperinCopper

Sulphate Solution—Estimation of Zinc in Zinc Sulphate

of Ironby Bichromate—Estimationof ChloridebyStandard

Soda—Estimation of Calcium Carbonate in a Mixture of

Chalkand Sand pp.131-139

QUANTITATIVE! ANALYSIS FOR ENGINEERS

Estimation of Iron in Iron Ores—Estimation of Sulphur and

Analysis forEngineers : Acidity and Alkalinity—Suspended

—

Permanent Hardness—OUs and Fats—Chlorides Calorific

Value of Fuels by Bomb Calorimeter—Analysis ofFurnace

Mortars:PhysicalTests—ChemicalAnalysis. Determination

ofPorosityof Brick. AUoys: Analysisof Brass, Bronze, &c.

PreparationofReagents pp.140-164

CONTENTS APPENDIX

TABLES OF USKFUL DATA

Elements and Physical Constants—III. Common Minerals

ofSubstances—V NaturalSilicates—VI SpecificGravityof

BuildingMaterials—^VII.FreezingMixtures—VIII.

—XII.CalorificValueofLiquidFuels—XIII.CalorificValue

of Gaseous Fuels—XIV Coal Analyses—XV Coal Tar

Pro-ducts—XVI AnalysesofFurnaceGases—XVII Analysesof

ExitGases—XVIII Approximate HighTemperatures—XIX.Temperaturesof Various Flames—XX Analysesof Natural

Waters—XXI Analyses of Boiler Incrustations—XXII

AnalysesofCylinder Deposits—XXIII.CompositionofAlloys

—XXIV Useful Numerical Constants— XXV. Tension of

Aqueous Vapour pp.165-187

SCOPE OF THE BOOK

While the programme of work herein outlined is intendedprimarily for engineering students, it includes a completecourse for builders and others who may be pursuing a shortcoursein the Chemistry of BuildingMaterials

The students using this book may be divided into three

classes:

—

1. Those able to devote three sessions to practical work,each session being made up of thirty-six periods, and eachperiodconsistingoftwohours

Such students shouldwork throughChapters I toVII in

the first session, and in the second session Chapters VIII

toXII

Chapter XIII will provide abundant material for thethird session

2. Those ableto devote two sessions tothe work mayomit

those experiments in the book which are carried out and

programme Should further deletion prove necessary, they

may, in working through Chapters XI., XII., and XIII.,

confine themselves to those experiments marked with anasterisk

3. Thoseable to devote one session onlyto the work, willfinda complete courseby carrying out only those experiments

in the bookwhich are markedwith an asterisk. This grammeisthe oneto befollowedbystudentstaking a course

pro-inthe Chemistry of Building Materials

ABBREYIATTONS USED

Ammon.(Am.) .

PRACTICAL CHEMISTRY FOR

intowhich these materialsmay be converted

For these " weighings" the balance is made use of, and

its importance in chemicalwork demandsafewexplanatory

remarksconcerning theprinciple onwhich itworks and the

manner ofusingit.

The mechanical principles underlying the construction of

thebalancecannotbediscussedherein full,andtheworkeris

referred to text-books on physicsfor a detailed description

ofa delicate balance

The illustrationon p. 2shows allthe visible portions,and

it will be noted that there is a beam of rigid but light

material, with arms of equal length, which oscillates on acentralknife-edge In using such an instrumentfor obtain-ing weights, we really compare the attractive forces of

gravitationontwobodies One ofthese bodiesisa standardweight, and when the attractive force is the same in each

tends to rest. The centre of gravity of the system (pans

and beam) is vertically beneath the central knife-edge onwhich thebeamswings; sothat,whenthe bodiesin thepanshavethe sameweight, a pointer at rightanglesto thebeam

mark

2 CHEMISTEY FOE ENGINEEKING STUDENTS

In order that the knife-edges may not become unduly

worn, a rest is provided in the shape of the support hh

knife-edge, while at the same time the knife-edges which

support thepans arerelieved frompressure

<^ \m A

Fig.l.—[FromThxn-pe's " QuantitativeChemicalAnalysis.")

a aisthebeamofthe balance,which consists of an acute

rhomboidoflightand rigid material

6 &is the horizontal supportwhich is raised and lowered

by the lever s. When this support is raised it keeps thethree knife-edges, k k k, just free, by slightly raising the

beamand thetwoscale-pans

Thestandardofweightusedisthe gram, whichrepresents

one-thousandth part of the " standard kilogram"

WEIGHING 3

The further relation exists, that 1 gram represents the

weightof 1 c.cm ofwaterat 4° centigrade

Thisfollowsfrom thefactthat1kilogram ofwater occupies

1 cubicdecimetre,and therelations are:

There are 100centimetres (cms.) in 1 metre

Therelationsbetween metricandBritishsystems are given

A setofsuch weights is shown,insitu,in Fig 2.

Thelargerweightsaremadeofbrass,and are designed somay graspedby

4 CHEMISTEY FOE ENGINEEKING STUDENTS

The weights representing decimal fractions of one gram

aremade, usually, ofaluminium

Although small weights representing the third decimal

figure are included, it is usual to obtain this degree of

accuracy with the rider.

This is a light wire stirrup which can be placed at anyscaledivisiononthe rightside of thebeam Itisobviouslythe lastweight to be adjusted when a bodyis weighed,and

thenumber ofthe scale division on which it rests gives the

third decimalfigure.

The actual value of each weight is marked upon it (see

compartment.•

Rules for Weighing.— To facilitate weighing, and to

pre-serve the good qualities of the balance, the following rules

should beobserved:

—

1. Neverput anythinguponthe pans,orremoveanything,

untilthe leveris set, sothatthebeamis atrest.

2. Place the body to be weighed on the left pan and theweightson theright

3. Putthe unit weightsinthe centre ofthe pan

Putthe 1stdecimalfigureweightsonthe rightside.

Putthe 2nddecimalfigureweightson theleft side.

Toget the 3rd decimalfigure, use therideronthe right

sideofthebeam

4. The bodies are of equal weight when the pointer

5. No substance should ever be placed directly on thepan, but should rest on a watch-glass or other suitablereceptacle

6. Form a habit of placing the weight-box as near aspossible totheright-handscale-pan, sothat you mayalways

use the right hand for manipulation of weights, while the

lefthand restsonthelever-screw, servingto raiseand lowerthebeam

7. Always pick up the weights withthe forceps provided,

8. Before replacing the weights in the box,always count

upthe valueoftheemptyspaces Thisaffordsareadymeans

ofcheckingthe value obtainedbyreading the weightsonthe

-Thefollowing measuringvessels are usedin chemical work,

and they are graduated to contain thecorrect

volumesatordinaryroomtemperature,15-5° C

The Grraduated Cylinder.— A cylinder of

thevolumeof liquid insidemay beread off.

These are made generally in sizes of 100

ccms., 250 c.cms., 500 c.cms., or J litre, and

1000c.cms., or 1 litre.

These cylinders have intermediate

their maximum capacity They are made to

contain the volumes of liquid represented by

theirmarkings

The Burette.—Thisisa glass tubeof about

1^ cms bore, graduated in cubic centimetres

and tenths, and possessing a maximum

capa-city of 50 c.cms It is used for delivering a

measured volume of liquid by opening the

tap or clip which closes the lower end The

figure shows one burette clampedin a burette

stand

The Pipette.—Thisisa glass vesselusedfor

delivering an exact volume of liquid. It has

only one graduation mark on it, and

conse-quentlyisonly used for deliveringexactly the

volumeofliquidmentioned on the instrument

Pipettes are made to deliver 5 c.cms., 10

c.cms.,15c.cms.,20 c.cms.,25 c.cms.,50c.cms.,

and 100c.cms

The liquid isdrawn above the mark bysuckingatthe top

end and then quickly covering the opening with thefinger.

Dropsarethenallowedtofalluntilthemarkis justreached

The Measuring Flask.—These flasks are made to hold

100, 250, 500, and 1000 c.cms exactly, and are not usedfor delivering at all. A graduation mark on the neck

Fig 3—{FromNewth's"Ele-

inentary

Prac-tical

Chemis-try.")

6 CHEMISTRY FOR ENGINEERING STUDENTS

to give the volume inscribed on the flask. The liquid in

these flasks is shaken by holding the stopper firmly and

invertingtwo orthreetimes

Fig i.—[From Newth's"Elementary Fig 5.

—

(FromNewtKs

ofthemeniscusmustbenoted.

General Practical Methods

Solution.— Whentwoormore substances bymixing, yield

a completelyhomogeneous substance (identical in all parts),

themixtureistermeda solution

Solutionsmaybesolid, liquid,orgaseous

More generally,the expression is applied to the case of

present in large excess, and the solid becomes completely

dissolved and disappears from sight. The resultant liquid

is clear and transparentinallparts, and no evidence of theexistence of the solid is apparent unless it colours the

solution Examples of solution are salt or sugar dissolved

GENEKAL PEACTICAL METHODS 7Evaporation.—Evaporation takes place at the surface of

liquid volume becomes less and less, and may ultimately

disappear

Anysolidwhichwasdissolved inthe liquidremainsbehind,

forminga residue

The process of evaporation is accelerated both byrise of

temperatureand byincreasingthesurface exposedtotheair.

For this reason a liquid is always evaporated in a shallowdishwhichstandson a sand-bath, a wire gauze,ora hot-waterbath

Crystallisation.—Crystallisation takes place when a clearsolutionofa substance is evaporated,soas to driveofifexcess

ofthesolvent Bytheremovalofsolvent, the solution

ulti-matelybecomes" saturated,"and oncoolingsuch a saturated

solution most of the dissolved solid crystallises out Therule to be observed when crystallising a clear solution is :evaporate by heating, until crystals begin to form on the

surface of the hot liquid; then remove from the source of

heatandallow to cool. Whenquitecold drainofiftheclear

mother-liquor, and dry the crystals by placing them on a

filter-padorporousplate

Precipitation.—Frequently, when two clear solutions are

mixed together, a separation of solid matter takes place.

The resultant solid,which gradually falls to the bottom of

precipitation

Decantation and Filtration.— When asolidinsuspension,

i.e. a precipitate,settles to thebottom of theliquid readily,

it may be separated from the liquid by pouring off, i.e. canting, thelatter. The solid remains behind atthebottom

Filtration is a more complete method of separating a

precipitate (ppt.) from the liquid in which it is suspended

Themixture ispouredon toa filter-paperfitted in a funnel,and theliquid runs through, while thesolidremainsbehind

Tofitafilter,the circular filter-paper is folded to form a

semicircle This is then folded again to form a quadrant,

and by opening the paper, folded in thisway, ahollow cone

is obtainedwhich can befitted into a glass funnel When

8 CHEMISTEY FOR ENGINEERING STUDENTS

(Pig 6). The liquid must never reach quite to the top of

the filter-paper, and one lot should run right through

before fresh liquid is added, especially when the work

is quantitative The liquid must be poured in carefully,

not "splashed" in, and when the work is quantitative thepouring must be done by the aid of a glass rod, to

prevent splashing and also to prevent drops of liquid and

Fig 6.—(From Newth's

"Elementary Practical

Chemistry.")

FlO 7.—{FromNewth's

"Elemen-tary Practical Chemistry.")

precipitate from running down the side of the beaker(seeFig 7). If the ppt on the filter-paper is to be washed,this is accomplished by a well-directed stream of distilled

water from a wash-bottle (see p 12). All ppts should

other-wise directed Thisaccelerates the rate of flowthroughthe

funnel, and this end is also reached by always making the

leg of the funnel touch the side of the receiving vessel, asindicated inFig 6. Anysplashingis also preventedby such

an arrangement

GENERAL PRACTICAL METHODS

A third method for quick-drying is to

place the filter and funnel in a tin cone,

which rests on a wire gauze (Fig 8). By

placing a small flame underneath, the filter

is soon dried completely

Crystals may be dried by first well

drain-ing, and then placing on a filter-pad or

between two sheets of filter-paper If they

are well drained it is seldom necessary to

placetheminthehot oven,andafinaldrying

maybeaccomplishedbywell pressingbetween

dryfilter-papers

Desiccation.—Desiccationis a processofdrying a substance

orkeepingit in a drystate, byplacing itin a vessel which

contains some material having a great affinity for water

vapour Sulphuric acid and calcium chloride are such

materials, and they are spoken of asdesiccating agents The vessel used

is called a desiccator (Fig 9). The

dryer is placed at the bottom of the

desic-cated rests onashelfin the centre of

thedesiccator The jointbetweenthe

lidandthevessel ismade air-tight by

greasingwithvaseline

The Bimsen Burner.—This form oflamp is used in all chemical experi-ments which require heating on a

¥m.9i.-{From.^'Newth's Smallscale. The aii-hole at the baseManual of Chemical can be varied in size, and by_ this

or non-luminous The latter is thehotterflame,andis usedfor all strong heating; it possesses

the further advantage that it deposits no soot. This flame

is obtained when the maximum amount of air mixes with

when

10 CHEMISTEY FOE ENGINEERING STUDENTS

pletely an ordinary luminous coal-gas flame is obtained.With the air-hole open, the flame has a 3-cone structure.Theoutermantle isthezoneofcomplete combustion and thesource of heat, the hottest portion being in the region A.The inner cone, B, consistsofunburnt gas,and is compara-tively cool (Fig 10). It is surroundedby the bluecone, D.The outer mantle has an oxidising action since it is mixed

with air in excess, and small objects like borax beads and

flame colouration wires should be held near A, the hottest

partoftheflame Thereducing flameisobtainedbyshutting

at C This small luminousareais suitable forreducingborax

GENEKAL PRACTICAL METHODS 11

Fig 12.

—

{FromThorpe's

In order to get a luminous reducing-tip,the nozzle must

be held a little wayfrom the burner, and theair-blastmust

notbeso strong

To Bend Glass Tubing.—For this purpose an ordinary

luminous "fish-tail"

bur-ner is used The glass

tube is held by the ends

in the manner indicated

in Fig 12, and

continu-ally rotated As soon as

softening commences,

re-move the tube from the

flame and bend it to the

desiredangle Sharpends

ofglasstubing or rod maybe rounded,by rotating them in

theBunsenflame

Ignition Tubes.—These can be made byselecting apiece

ofglasstubing 15 cms.long,and having adiameterof0'7 to

0-8cm The endsshouldberounded,

and then the tuberotated with itscentreina Bunsenflame When the

glassisthoroughly

quickly and allow

flame, and, while

thickened portionis blown out byapplying themouth tothe

open end In this way twoignition-tubes will be produced.(SeeFig 13.)

Cork Boring.—Holes are bored through corks by means

of a cork-borer The edge must bethoroughly sharp before

:> c

ocz

Fig.13,

12 CHEMISTRY FOR ENGINEERING STUDENTS

to be relied on rather than pressure Excessive pressure

alwaysleads to a tearingof the cork, especially if the borer

or methylated spiritcontaining a littlesoda

All ordinary corks must be softened before boring, by

rollingthemonthefloor, withthefoot.

The Wash-bottle (see Fig 14).—The

capacity of the flask should be about

then two holes bored side by side. Thefigure indicatestherelativelengthofeach

tube, and also the angle most suitable

To the end of the acute-angled tube a

nozzleisattachedby rubbertubing Thenozzlecanbemadeby drawing outa piece

of glass tube of the right diameter Allends shouldbe roundedby rotation in the

Bunsen flame before finally fitting thepartstogether Byblowingdownthe shorttube a fine jet of water can be directed

fromthenozzle

In order to facilitate the holding of the washing-bottle,

when itcontainshotorboilingwater, awrappingoftwineor

thread maybeplacedroundthe neck

To Out Glass Tubing.— Make a cut at the desired place

with a sharp triangular file, then place the file on thebench, rest the glass tube on the edge of the file withthe

cut uppermost, and press gently on each side of the cut.

The glass tube will snap neatly in two pieces at the

file-mark

Platinum Wire.—This must be a piece about 10 cms

long It is fixed in a piece of drawn-out glass tubing,

by rotating the tube with the wirein position, ina Bunsenflame

GENERAL PRACTICAL METHODS 13

tions in which the solid is taken upon thewire, a loop, B,

shouldbeused (Fig 15).

Stirring-rods.—These are made of glass rod, and theyshould be of such

length, that a rod i -^ ^

inuse extends only

one or two inches „

the vessel used Fig.15.

Two of each size

should be cut,namely, 7, 12, and 18 centimetres in length,

and theirendsrounded byrotation intheflame

A rod should be usedwhenever a liquid hasto be stirred,

in Fig 16. Ignition

at a bright red-heat

for 15 to 20 minutes

isusuallysufficientto

drive off all tracesof

moisture,butitshould

berepeated untiltwo

consecutiveweighings

agree

When the crucible

has cooled slightly, it

must be transferred

to a desiccator bymeans of crucibletongs When quite cool, it is removed from thedesiccatorandweighed

Some of the ppt will always adhere to the filter-paper,and thismustbe burnt byrolling the paperinto a smallroll

with the ppt wrapped inside The platinum wire is thenFio, 16.

—

(From Newth's" Manualof

ChemicalAnalysis.")

14 CHEMISTEY FOE ENGINEERING STUDENTS

wound roundit(Fig 17),andwhile held thus thefilter-paper

is burnt by placing it in a flame It catches light,and is

then withdrawn from the burner, and allowed to smoulder

1

Fig 17.

—

{From Newth's"ManualofChemicalAnalysis.")

out. During this process,the burning filter must be heldover the uncovered crucible, which contains the rest of

the ppt The crucible itself must rest on a sheet of

glazed paper,so that any spilled portions may be collected

without loss. When the filter has been

com-m pletelyburnt, the ash and the adhering ppt are

^ carefullytappedintothecrucible Theweightof

the ash, due to thefilter-paper itself, mustinall

cases bedeductedfrom thefinalweight

treat-mentbeyondthatmentionedhere,fulldetails will

begiveninthe QuantitativeSection

Test-tnbes are used for boiling or warming

smallquantitiesof liquid. Forthis purposethey

maybe held directly in the flame in a slanting

position Test-tube holders are often suppliedto

\^_^ preventburningthefingers,buta veryserviceableFia.18. ^^^ ^®®®clumsyholdercan bemade by wrapping

a pieceof post-card round the upper end of the

tube,andholding thefree endstogether, as in Fig 18.

Test-tubes are kept in a rack, inwhich they stand inan

upright position The best rack isonefittedwith awooden

afterwashing

GENEKAL PKACTICAL METHODS 15the cupboard It is much easier and quicker to wash out

apparatus immediately after use than after standing for

several days The test-tube brush shouldbeusedfor

clean-ing test-tubes and boiling-tubes If water fails to removestains,try in turn hydrochloric acid, nitric acid, or causticsoda If the cold liquids are not sufficiently active,theyshouldbe heated

To Cut Glass Tube of Wide Bore.— When tubing has adiameter greaterthan 1-5cms it isnot easilybroken, bythe

methodexplainedonp 1 2,especiallyif itbeofhardglass. The

following method must be adopted: Make a deep file-mark

at the desired place, and in thedirection whichthebreakisrequired to take Next makethe end of a drawn-outpiece

ofglasswhitehot, in theblowpipeflame, andplace it quickly

onthefile-mark

This procedure will start a crack round the tube,and ifnecessary theprocess may berepeated tocompletethecrack.The Collection of Gases.—Gases may be collected in gas-

are not appreciably soluble in that liquid, e.g. oxygen andnitrogen Those gases which are soluble in water to a

marked extent must be collectedby eitherupwardor warddisplacementof air. The upwarddisplacementmethod(see Fig 45) is suitable for gases lighter than air, such asammonia; while downward displacement must be used (see

down-Fig 33) when the gas is heavier than air, e.g. chlorine and

carbon dioxide

itmust be coveredwithaglass platewhichhasbeen greased,

inorder tomakethejoint gas-tight

The jar of gas may then beputaside ina coolplace until

it isrequiredfor use

Kipp's Apparatus for Generating Gases.—This apparatus,

shown in Fig 19, should be used wheneverpossible for

pro-viding a steady stream of gas The parts are as followsThecompartmentsB and Caremadeinonepiece; theformercontains thesolidsubstance,andthelatter acts asareservoirfor the acid used The two compartments communicatebymeans of anarrowneck, and eachone is fittedwith a tubule

andstopper

The topmost part A consists of a large bulb, drawn out

16 CHEMISTEY FOE ENGINEERING STUDENTS

belowinto along, taperingtube,andwhen placedin position

it fitsperfectly intotheground neckof B,makingagas-tight

joint.

The apparatus is charged for delivering a steady stream

of COg as follows: Small lumps of marble are introduced

into B,while A is held loosely in position so as to prevent

themarble falling into 0 When B

ishalf-filled,theupperpartA isfixed

in position and the hydrochloric acid

is poured into it,while the tap k is

keptopentoallow the escapeofair.

The acid runsintoC, andthelevel

is allowed toriseuntil it reaches themarble Thetapkisthenclosed,and

closedandtheacidattacks the marble,the pressure of COg produced, forces

the acid down until gas ceases to

be evolved In this manner B and

part of C become filled with the

gas,whichforces theacidpartlybackintoA

The apparatus thus regulates

from k the pressure falls, and acid

•p, ,g isallowed to act on the marble once

more

Kipp's apparatus may be used for generating a steady

streamofthe following gases:

—

Gas.