258 ON THE PURIFICATION OF DRINKING WATER. 
gives the preference to oxalate of potassa. He first ascer- 
tains the degree of hardness of water, and then adds the 
requisite quantity of oxalate of potassa, by which an oxa- 
late of lime is precipitated, and there remains in solution, 
instead of the lime displaced, a carbonate, sulphate of pot- 
ash or chloride of potassium, as the case may be, and the 
water is purified and fit for use. 
The following equation explains the reaction of oxalate 
potash (we assume the salt to be neutral) on bi-carbonate 
of lime : 
CaO,2C0 2 -f^aO,S034-2(KO,Ox) = 2(CaO,Ox)+KO,2C02-|-KO,S03 
Bicarbonate Sulphate Oxalate of Oxalate of Bicarbonate Sulphate 
of lime. of lime. potash. lime. of potash, of potash. 
Mr. Horsley's patent process does that which Professor 
Clark's fails to do : it decomposes all the earthy salts on 
which the hardness of water usually and mainly depends. 
But it is open to still greater objections than those that 
have been raised to the other method. Besides being like 
Clark's process virtually impracticable, it would prove very 
expensive, and as regards the metropolitan river waters it 
is quite unnecessary. Moreover the idea of " physicking" or 
" doctoring" the water by the addition to it of a poisonous 
agent, would, if even no other objection existed to this 
scheme, be quite fatal to it. For though in the hands of 
competent persons ^iike Mr. Horsley, no possible injury 
could arise from its use, yet the public would always have 
some suspicion of water thus treated ; and as a certain 
English engineer once observed to Arago, " Water, like 
Caesar's wife, should be above suspicion. — Pharmaceutical 
Journal, April 1, 1850. 
