690 SCIENCE PROGRESS 



plicably large amount of what appears to be limestone-stuff? 

 Now, we can take water such as is available in this district and 

 ascertain whether the solid which is deposited on boiling it is 

 in reality limestone-stuff; but will it not be well first to boil the 

 solution prepared by passing the gas into the lime-water to see 

 how it behaves ? It soon appears that it behaves like a natural 

 hard water. On the other hand, the deposit from a hard water 

 — the fur from a kettle or boiler — behaves exactly like limestone 

 when burnt and towards acids. May we not, therefore, also 

 expect that the hard water will contain the limestone-stuff gas ? 

 As soon as the idea that such may be the case is evoked in our 

 minds, it occurs to us — since the limestone-stuff is deposited on 

 boiling the water — to boil hard water and pass the steam into 

 lime-water : a precipitate soon appears and, therefore, we can 

 write O.E.D. — as at the conclusion of an exercise in geometry. 

 The gas is obviously soluble in water : we take boiled water 

 which is not rendered turbid by lime-water and pass in the gas 

 — lo and behold ! on adding lime-water the precipitate appears. 

 But the deposit forms in water-bottles without the water being 

 heated : may we not, therefore, infer that the solution of the gas 

 in water is an unstable one — may we not expect to find the gas 

 in the air ? Does not this question recall to our recollection the 

 fact that when we have carelessly left clear lime-water exposed 

 to the air a deposit has collected on the surface ? Does not this 

 serve to suggest the experiment of exposing a considerable 

 quantity of lime-water to air so as to obtain sufficient solid for 

 examination ? When the experiment is made, sufficient solid 

 having been obtained and examined, we soon satisfy ourselves 

 that it is chalk-stuff: consequently that air does contain the gas, 

 although in relatively small amount. 



But the magic circle is not yet complete. We speak of lime 

 as made by burning limestone : is this correct — do we burn it 

 as we burn wood and coals and other things ? You reply, 

 " Perhaps not ; we can kindle wood and coal and when once 

 on fire they continue to burn — limestone will not take fire ; it 

 is baked rather than burnt." We have learnt that it is simply 

 resolved into two other materials by this baking — what becomes 

 of wood and coal when burnt ? Seemingly they are destroyed 

 — but has not our experience with limestone taught us to be 

 careful : that disappearance does not necessarily mean destruc- 

 tion? What do we know of the burning of coal — what does 



