84 WRITINGS OF JAMES SMITHSON. 



of copper placed in it on the silver is preferable to a solu- 

 tion. To find chlorine in milk, I put some sulphate of 

 copper to it, and placed a small piece of bright silver in the 

 mixture. 



3. Phosphoric Acid. The alkali containing it, after satu- 

 ration by acetous acid, gives a sulphur-yellow precipitate 

 with nitrate of silver, which no other acid does. The pre- 

 cipitate obtained with lead crystallizes on the blow-pipe. 

 M. Berzelius's elegant method of detecting phosphoric acid 

 is universally known. 



4. Boracic Acid. Its presence in carbonate of magnesia, 

 and in some other of its compounds, is indicated by the 

 green colour they give, during their fusion, to the flame of 

 the lamp. 



M. Gay-Lussac has observed that a solution of boracic 

 acid in an acid changes the colour of turmeric paper to red, 

 like an alkali.* Borax, to which sulphuric acid has been 

 put, does so, and the same is of course the case with a bead 

 of soda containing boracic acid. 



The most certain test of boracic acid in a soda bead, &c., 

 is to add sulphuric acid to it and then spirit of wine, whose 

 flame is coloured green, if boracic acid is present. 



5. Arsenical Acid. Alkali containing it produces a brick- 

 red precipitate with nitrate of silver. f 



6. Chromic Acid. Chromate of soda and its solution are 

 yellow, and so is the precipitate with lead. That with silver 

 is red. 



Chromate of soda or potash fused on a plate of clay leaves 

 green oxide of chromium. 



Chromate of lead fused on a plate of clay produces a very 

 dark-green mass, which is probably chr ornate of lead ; with 

 an addition of lead, it forms a fine red, or orange glass. 



Lead added to the green oxide left by chromate of soda 



* Annales de Chimie et de Physique, tomo xvi. p. 76. 

 f Annals of Philosophy, N. S. vol. iv. p. 127. 



