the Substances usually present in Water. 39 



separated from this precipitate will shew muriatic acid on adding 

 nitrate of silver. Nitric acid, which may be looked for in all surface 

 water in India, is indicated by concentrating the water by evapora- 

 tion, and adding gold leaf, muriatic acid, and boiling it, or better, 

 by adding a little pure sulphuric acid, free in particular from nitric 

 oxide gas, which almost all ordinary sulphuric acid contains, and 

 putting into it a small crystal or two of pure green proto- sulphate 

 of iron, and applying heat, upon which, if that acid be present, a 

 dark greenish hue will soon pervade the liquid in the neighbourhood 

 of the crystal. Vegetable acids or other matters, such as crenic 

 acid in springs, and vegetable infusory matters in surface waters, 

 will blacken on exposing to heat the residuum of the evaporation of 

 the water ; and if animal matter be also present, ammonia will be 

 evolved, shewn by the cloud formed beside a rod dipped in muriatic 

 acid and held over it, or more delicately, by reddening the yellow of 

 moist turmeric paper also held above it. Some of these substances 

 when in solution also give a brown precipitate with nitrate of 

 silver. 



The residuum of evaporation, if boracic acid, met with in some 

 waters, be in it, when mixed with a little sulphuric acid will tinge 

 burning alcohol of a beautiful green, not the bluish green given in 

 the fire by common salt. Iodine, though in minute quantity, will, on 

 making thin solution of starch with the water nearly boiling, and 

 cooling it, give with a little chlorine water, or even with nitric 

 acid, a blue film where the two different liquids touch each other. 

 Bromine, to be looked for in salt waters, is best detected by heating 

 in a test tube with pure sulphuric acid the precipitate from the wa- 

 ter by nitrate of silver, when reddish or yellowish-brown vapours of 

 bromine, like those of nitrous acid, will be evolved. 



The bases of the salts usually present in water may be detected as 

 follows : — Lime by oxalate of ammonia, a white precipitate in a 

 somewhat diluted solution. Magnesia, in the water from which the 

 lime has been thus separated, by a white precipitate on the addition 

 of carbonate of ammonia and phosphate of soda or ammonia. Alu- 

 mina, provided no peroxide of iron be present, by acidulating the 

 water, and adding carbonate of ammonia with constant stirring, so 

 that the liquid may be strongly charged with free carbonic acid, on 



