1839] 



On Chemical Tests. 



287 



civ. Certain nitrates are occasionally present in water. Nitrate of 

 lime will be taken up from the residue of evaporation by alcohol, and 

 may be decomposed by carbonate of potassa, so as to afford carbonate of 

 lime and crystals of nitre. 



cv. It sometimes happens that water contains lead, which may be 

 detected by evaporation to one-eighth its bulk, adding a few drops of 

 nitric acid, and then sulphate of soda, which gives a white insoluble 

 precipitate; and sulphuretted hydrogen, which forms a black cloud. 

 These precipitates may be reduced by heating them before the blow-pipe 

 upon charcoal, mixed with a little black flux. 



cvi. If vegetable or animal matte?' be contained in water, it gives 

 it a brown colour, especially when evaporated. It may be destroyed in 

 the dry residue by igniting it with a small addition of nitrate of am- 

 monia. 



cvn. Iodine and Bromine must always be sought for in mineral 

 waters. Where they are suspected, the water should be evaporated to 

 dryness, and the residue triturated with a little distilled water, which 

 will take up the iodic and bromic salts, they are recognized by the ad- 

 dition of a solution of starch, having previously added a few drops of 

 solution of chlorine ; the iodine will turn blue, but if no iodine be present 

 the chlorine will turn the bromine of a yellow tint. 



A DICTIONARY' 



OR ALPHABETICAL LIST OF 



1- ACID acetic, detects resin and gluten which dissolve in it, but 

 on the addition of water the resin precipitates: the gluten does not. 

 See 103. Acetic acid dissolves camphor, and essential oils ; and com- 

 bines with earths, alkalies and metals, forming the class of salts, called 

 acetates. These salts are decomposed by strong sulphuric acid, which 

 liberates the acetic acid, when the latter may be detected by its well known 

 odour, which is that of strong vinegar, see 18 a. 



a Acetic acid may be contaminated by sulphureous and sulphuric 

 acids ; they may be discovered by their proper tests, see 40,. and 70 a. 



