84 DR. R. ANGUS SMITH OX THK EXAMINATION 



When animals decay, tliey must, according to the above 

 analyses, give out much more common salt than the same 

 amount of vegetable matter ; and this we find to be the 

 case in the drainage of grave-yards. But it is from living 

 animals we find the greater amount of common salt : that 

 which goes into the blood is rapidly thrown out ; and as 

 we take with our food amounts varying from lOO to 250 

 grains of common salt per day, let us say 150, an equal 

 amount must be abstracted from us. It is for this reason 

 sewage-water constantly is found to contain common salt, 

 increasing according to the amount of sewage. For this 

 reason common salt is found in the saltpetre of all countries. 

 It is a part taken from the blood of the dead or the living- 

 animal remaining with the nitrogen unchanged, even when 

 the organic matter has been so highly oxidized that nitric 

 acid takes the place of albumen. 



Pure spring-, or very fine stream-water gives only a 

 slight precipitate with nitrate of silver. This has a bluish 

 tinge, not being dense enough to become white. When 

 there is more than this slight precipitate, nitric acid is 

 generally found, especially if the water has passed through 

 porous materials. 



These tests must be used and the inferences drawn with 

 great discretion. We know that near the sea there may 

 be found a certain amount of chlorides in the springs, rising 

 according to circumstances, until the water becomes brine. 

 The same thing occurs near great deposits of salt, such as 

 in Cheshire and elsewhere. There are also saline wells 

 scattered over most countries, the origin of whose chlorides 

 is quite unknown to us. There is in the rain driven 

 violently from the sea an amount of common salt sufficient, 

 on crystallizing, to dim the windows of houses many miles 

 inland. In manufacturing- towns where coal is burnt, the 

 rain contains more chlorides than rain in the country. 

 Many large districts of tropical countries contain nitrates 



