582 Proceedings of the Royal Irish Academy. 



may, in part at least, have been attributable to the impurities or 

 adulterations of the chloroform, or of the chloral hydrate employed. 

 I^ow, as I find that neither chloroform nor chloral hydrate, in their 

 pure condition, have any apparent action on the molybdic test, but 

 that many of their usual impurities develope the blue reaction, it 

 aiiords us a ready means of testing their purity. Thus, as regards 

 chloroform, one of its common impurities is ethylic alcohol, which 

 it may contain either from imperfect preparation, or from fraudulent 

 addition, the very high price of chloroform offering a great temptation 

 to the unscrupulous vendor to increase its bulk or weight by the addi- 

 tion of alcohol, which so readily mixes with it. I have found that 

 the molybdic test at once enables us to detect such an adulteration, 

 even where it occurs in very small proportions in chloroform. Thus, 

 in one experiment, I mixed one part of rectified spirit with a hundred 

 parts by volume of pure chloroform, and one drop of this mixture 

 being brought in contact with three or four drops of the molybdic 

 solution, previously warmed in a Avater-bath, gave an immediate deep 

 blue colouration from the spirit contained in it ; and, in a second ex- 

 periment, with a mixture of one part of spirit to a thousand parts of 

 chloroform, a single drop of the mixture, being similarly treated, 

 developed a faint blue reaction. Indeed, so searching is this test 

 as regards the purity of chloroform, that I was unable to obtain any 

 sample of that substance in commerce sufficiently pure not to give 

 a blue reaction with the molybdic test, owing to the minute quanti- 

 ties of volatile oils, and other impurities, they contain ; and for my 

 experiments I was obliged to repurify the commercially pure chloroform 

 to obtain a sample which would give no coloured reaction with my 

 test. 



In the case of chloral hydrate, it is stated that one of its usual 

 impurities is the chloral alcoholate (a compound in which alcohol, 

 instead of water, is combined with anhydrous chloral), and that 

 this substance has somewhat different effects on the system from 

 those produced by the hydrate. This compound, owing to the 

 alcohol it contains, gives the blue reaction with the molybdic test, and 

 I have found that where the chloral hydrate contained even so small 

 a proportion of the alcoholate as one part in a thousand parts, a 

 little of such a sample, being taken, indicated its presence wlien 

 examined by the molybdic test ; and it is probable that some of the 

 other impurities which are met with in this important substance may 

 be similarly detected. 



Those two examples are sufficient to indicate the use to which this 

 test may be applied in the determination of the purity of different 

 substances used in medicine, as well as in scientific research. 



Finally, I would remark that, as the reaction of molybdic acid 

 on ethylic alcohol is so sensitive and prompt in its action, I entertain 

 the hope that there may yet be founded on it, not merely this qualita- 

 tive test, but likewise a means for the quantitative determination of 

 that important alcohol. 



