86 Notes on Chemistry, &/-c. 



A scale of the salt introduced into a drop of the acid no larger than 

 a pin's head will show the effect distinctly. 



The acids in which I have found the salt to redden are, sulphuricj 

 hydrochloric, hydrofluoric, chromic, phosphoric, (if slightly diluted,) 

 and the common vegetable acids, such as oxalic, tartaric, citric and 

 acetic acids. 



I have found it to blacken with chlorine gas, solution of chlorine, 

 (recently prepared,) bromine, sulphuretted hydrogen, nitrous acid 

 vapors, and nitric acid. 



It is highly probable, that it would be blackened by bromic acid 

 and chloric acid, and possibly by iodic acid, but I have not at pres- 

 ent these acids in a free state to determine their action ; the method, 

 however, in which I use the test will prevent any fallacy from the 

 presence of chloric, bromic, iodic or chromic acids, and of sulphuret- 

 ted hydrogen. It is to evaporate the supposed nitrate to dryness, 

 and introduce into a tube retort A, (see the figure,) a small portion 

 of the salt, on which a few drops of sulphuric acid are to be poured ; 



then on applying moderate heat, by means of a spirit lamp, a portion 

 of the volatile products are to be driven over into the receiver B, in 

 which a few scales of the salt are previously placed. If these are 

 blackened, the salt is to be considered as a nitrate, provided the pres- 

 ence of those few substances which might cause the same result has 

 been guarded against. Now by the very method proposed, viz. 

 evaporating to dryness and adding sulphuric acid, the presence or 

 absence of chromic, chloric or iodic acid and sulphuretted hydrogen 

 will be determined ; for the color of a chromate, the evolution of per- 

 oxide of chlorine from a chlorate, the liberation of iodine from an 

 iodate, and the odor from a sulphuret, will at once decide with re- 

 gard to each. As iodic and bromic acids, even if they are found to 

 blacken the salt, are not sufficiently volatile to be driven over by the 

 heat to be employed, no error could arise from their presence. 



1 have observed, that if the salt used above, or the bi-iodide of 

 mercury itself, be introduced into a test tube, with strong sulphuric 



