688 SCIENCE PROGRESS 



invariably a crust is formed in the kettles and boilers in which 

 it is heated. It is said vaguely that the water contains lime and 

 such deposits are often referred to as " lime out of the water." 

 In most households it is known that although the deposit from 

 the water sticks hard to a bottle and cannot be simply washed 

 out, it is easily removed by acid, even by vinegar. Is it right 

 to speak of a natural water as containing lime? How comes 

 it that acid removes the deposit referred to? Surely such 

 questions may be answered by a few simple experiments — the 

 solubility of lime is easily contrasted with that of limestone, 

 their comparative behaviour with acids easily examined. It 

 turns out that lime is much the more soluble in water and that 

 limestone is scarcely soluble at all, to a far smaller extent than 

 will account for the amount of solid dissolved in hard waters ; 

 the solution of lime is quite unlike any ordinary water, peculiar 

 in taste and in many other ways. Acids are found to dissolve 

 both lime and limestone with extraordinary ease but to affect 

 them very differently, the former disappearing quietly although 

 the liquid becomes very hot, whilst the latter disappears with 

 much spluttering and fizzing— something being forced out from 

 the seething mass. It is easily ascertained that a gas is given 

 off. A prudent man desires to know how much money he 

 spends — to know merely that his cash balance is diminishing is 

 not enough : the scientific inquirer will not be satisfied with the 

 observation that something escapes on dissolving the limestone 

 in acid but will question how much. It is as easy as not to 

 make the experiment in such a manner that it affords rough 

 quantitative results. The loss in repeated trials with whitening 

 amounts to from 42-43 per cent, on the amount of the limestone 

 dissolved. 



The habit of putting two and two together is the one before 

 all others to be acquired. Thinking back, we remember that 

 the limestone lost about 44 per cent, in weight when burnt; 

 now we find that it apparently loses nearly as much when 

 dissolved in acid : is this a mere coincidence or has the 

 resemblance a deeper meaning? We have no proof as yet that 

 lime is precontained in limestone — none that the gas comes from 

 the limestone alone ; but it is at least conceivable that the loss 

 which it suffers when burnt is due to the gas which is given 

 off when the stone is dissolved in acid and which may be 

 collected easily. The conclusion is a legitimate one from the 



