306 REPORT—1890. 
substance is dispelled by heating and by dissolving the chalk in acid. 
The experiment is very easily carried out in a small bottle or conical 
flask provided with a tube to contain acid, and closed by a cork through 
which pass a narrow tube bent at a right angle and a small drying tube 
full of cotton wool. The chalk is weighed out on thin paper and dropped 
into the flask, a little water is poured on to it, and the acid tube is then 
introduced, after which the cork is inserted. The bent tube is closed by 
a smali stopper. On tilting the flask acid escapes and attacks the chalk; 
the spray is prevented from escaping by the cotton wool. When the 
action is at an end air is sucked in through the narrow bent tube to dis- 
place the chalk-gas, and finally the loss in weight is determined. Such 
an apparatus gives admirable results. 
7. Marble may then be examined in a similar way ; as it is found to 
behave both on heating and when dissolved in acid much as chalk does, 
it may be presumed to consist of chalk-stuff. Next, limestones should be 
taken ; the result obtained with them may be lower owing to their con- 
taining clay, &c.; but this is to a large extent rendered evident by insolu- 
ble matter left on treating with acid. Let the percentage of chalk-stuff 
in the limestones be calculated from the results which they afford, assum- 
ing the results obtained with chalk to be practically those afforded by 
pure chalk-stuff. Lastly, direct attention to the occurrence of crystals 
(calcite) in limestone rocks, to stalactites, &c.; show specimens, and have 
them examined: the results will show that they also consist of chalk- 
stuff. 
8. Having pointed out that chalk consists of shells, &c., of’ sea-animals, 
coral and shells of various kinds—oyster, cockle, limpet—should be given 
for examination ; all these will be found to give results from which it 
may be inferred that for the most part they consist of chalk-stuff. Egg- 
shell and lobster or crab-shell in like manner will be found to yield lime 
when burnt, and to behave much as chalk does towards acid, but the 
presence of a certain amount of ‘animal’ matter will be evidenced by the 
blackening on heating and the insolubility of a certain proportion in acid. 
9. Ordinary bone, gypsum, clay, and rocks other than chalk or lime- 
stone rocks are next given for study, in order that it may be discovered 
that the behaviour of chalk-stuff is peculiar and characteristic, and that 
there are many varieties of natural solids. Rough estimates of the 
amount of chalk in soil may be made by determining the amount of chalk- 
gas evolved on treating the soil with acid. 
10. In a hard-water district the residue from the water will probably 
look more or less like chalk ; its behaviour when heated with acid and 
when strongly heated should therefore be determined, and local boiler or 
kettle scale should then be studied as chalk was previously. 
11. In this manner a large number of data will be accumulated which 
render it possible to discuss the origin of chalk; to explain the presence 
of chalk-stuff in water and its withdrawal from water by animals, dc. 
The study of chalk in the manner indicated would make it possible 
for the student (1) to comprehend the principle of the method followed 
by chemists in characterising substances whereby they are led to discover 
distinct forms or species; (2) to realise not only that there are com- 
pounds, but also that such substances have a fixed composition; and (3) 
the entire difference in properties between a compound and its constitu- 
ents would have been brought out most clearly by comparison of chalk- 
See rete oo 
