2839.] 



On Chemical Tests. 



273 



pure water, stir it well, and filter. The clear liquid might then be 

 thrown into clean test tunes, or wine glasses. If reddened litmus paper 

 was dipped into one of them, and ihe liquid turned the paper blue, it 

 would indicate the presence of a carbonated, or of a free alkali. To as- 

 certain if carbonic acid was present, a little dilute nitric acid might be 

 dropped into the same glass ; should' effervescence occur, it would es- 

 tablish the fact of carbonic acid being present; but if there was no effer- 

 vescence, a free alkali may be assumed to be held in solution, and to 

 have changed the colour of the paper. 



xv. The solution might then be neutralized by nitric acid, and it 

 would be known to be in that state when it affected neither blue nor 

 reddened litmus paper ; or it might be made a little acid. A drop of 

 nitrate of silver might then be added, and if a white precipitate took 

 place that blackened in the sun, and that was soluble in ammonia, it 

 would indicate the presence of muriatic acid. 



xvi. If a drop or two of oxalic acid, or oxalate of ammonia, were add- 

 ed to the liquid in another test tube, and a white colour or precipitate 

 took place, it would indicate that lime was held in solution, 



xvii. If another portion of the liquid was now concentrated by evapo* 

 ration, and put aside to cool, perhaps crystals would shoot in it. If these 

 crystals deflagrated when thrown on red hot charcoal, they would indi- 

 cate that the earth contained saltpetre. 



xviii. If the crystals were removed from this concentrated solution, when 

 cold, and it was evaporated slowly to dryness, probably something like 

 common salt would be seen to form. And if the taste in some measure 

 corresponded therewith, it would, with the test of nitrate of silver, indi- 

 cate that the earth was a saltpetre earth, mixed, as it usually is, with 

 muriate of soda or common salt, and other substances. 



xix. The earth that remained in the filter might be next examined — 

 suppose dilute muriatic acid poured upon it dissolved a considerable 

 portion with effervescence, leaving only a quantity of sand behind. If 

 the acid solution gave a white precipitate with sulphuric acid, or oxalic 

 acid, it might be presumed that the earthy part which was insoluble in 



water was chiefly carbonate of lime, and sand. 



xx. I purposely abstain from going into niceties, because that would 

 involve a dissertation : whereas, to ascertain the chief qualities of the 

 earth is all that is here aimed at, or designed. 



xxi. But as some further insight into the method of examining an un- 

 known substance, may be desired by the young enquirer, I add the fol- 

 lowing directions from Rose, which I have re-arranged, and endeavour- 

 ed to make plain and intelligible. 



