272 



On Chemical Tests. 



[Oct, 



but who are either learning that science, or who occasionally employ 

 themselves in chemical investigations. 



X. Accum's Tests by Maugham gave me the first idea connected with 

 this compilation, and the index to his book formed an easy guide 

 for the alphabetical order which ^ I have adopted. His book and the 

 following works are those to which I have been chiefly indebted for the 

 information I have here collet ted and put together, viz. Rose's Analyti- 

 cal Chemistry translated by Griffin ; Henry's Chemistry ;Ure's Chemical 

 Dictionary ; New edition of the Encyclopaedia Briitannica ; Joyce's Mine- 

 ralogy; some chemical tables; the London and Edinburgh Philosophical 

 Magazine, and some other scientific Journals. 



xi. I should have been glad to have made the descriptive action 

 of the tests more satisfactory if I could, but chemical authorities I 

 find do not always agree, and there are some great discrepancies 

 among them. Besides, the colours and precipitates produced by 

 re-agents are very much influenced by quantity,, as well as by 

 foreign substances that may be held in solution, so that colours 

 especially, cannot always be correctly defined. If a test acted on a so- 

 lution of one substance only, and that substance was pure, no doubt 

 but its precise action and die colour of the precipitate might be correct- 

 ly delineated, but when an unknown compound is to be examined, the 

 direct object of testing is to ascertain the several substances that make 

 up the compound, and to arrive safely at this point it is necessary to 

 make use of several tests, especially of those that are distinctive, if such 

 are known, and to be had. 



xn. There are two methods of doing this, and by the two conjointly, 

 viz., by the blow pipe, and by re-agents, analytical investigations are 

 successfully performed- I have combined both, and have endeavoured 

 to attain the object in view as far as my means allowed. 



xiit. I presuppose that those who may use the following compilation 

 are acquainted generally with the proper methods of testing, and with 

 the use of the blow-pipe. But those who are not I will briefly put in 

 the way, premising only that the examples given are as plain and sim- 

 ple as I could make them; but not at all professing to go into the mi« 

 nute detail necessary when mineral or other substances are to be ana- 

 lized, and the quantities of their component parts are to be specified by 

 weight. 



xiv. Suppose an alkaline earth to be picked up, and you wished to 

 know what it consisted of. The first step would be to dissolve it* in 



«j 



* Or as much of it as is soluble. 



