Davy — On a Neiv CJmnical Test for Carbolic Acid. 155 



XXVI. — On a ISTew Chemicai Test foe Caebolic Acid, and its Useful 

 Applications. By Edmund "W. Davy, A. M., M. D., Professor of 

 Forensic Medicine, Eoyal College of Surgeons, Ireland. 



[Eeacl, May 13, 1878.] 



I had the honour, a short time ago, of bringing under the notice of the 

 Academy, and of publishing in these Proceedings,^ a new and exceed- 

 ingly delicate chemical test for alcohol which I had at the time dis- 

 covered ; and I pointed out some practical applications which might 

 be made of that test. 



I subsequently directed attention to some further useful objects 

 which may be attaiaed by the employment of that alcoholic test, 

 which latter have appeared in the London Pharmaceutical Journal for 

 last year. I have recently discovered that the reagent which I em- 

 ployed for the detection of alcohol in the test referred to, viz., a solu- 

 tion of molybdic acid or molybdic anhydride in strong sulphuric acid, 

 is a very delicate test likewise for carbolic, or as it is otherwise 

 termed, phenic acid, a substance which is now one of considerable in- 

 dustrial importance, admitting as it does of so many useful applica- 

 tions, and one for which it is desirable to have a ready and at the 

 same time a delicate test, for the detection of its presence under differ- 

 ent circumstances. I have observed that when a drop or two of a 

 dilute aqueous solution of carbolic acid is brought in contact with a 

 few drops of the molybdic solution stated, there is immediately pro- 

 duced a light-yellow or yellowish-brown tint, which, passing to a 

 maroon or reddish-brown, soon develops a beautiful purple colouration, 

 which latter remains without further change for a considerable time. 

 I should here observe that the application of a gentle heat will hasten 

 the development of the purple reaction, though it will take place, but 

 more slowly, at the ordinary temperature ; and it is the production of 

 this purple under the circumstances stated that constitutes the test for 

 carbolic acid. The molybdic solution which I have chiefly used for 

 this purpose is similar to the one I have employed for the detection of 

 alcohol, and is made by dissolving, with the assistance of a gentle heat, 

 one part of molybdic acid in ten parts by weight of pure and concen- 

 trated sulphuric acid. But the exact amount of molybdic acid dis- 

 solved appears to be a matter of indifference, as I have used other 

 proportions with success, and in some recent experiments I found that 

 a solution where there was only one part of molybdic acid in a hun- 

 dred parts of sulphuric acid acted very well. 



The mode of using this reagent is simply to add three or four drops 

 of it to one or two of the liquid under examination, placed on any 

 white porcelain or delf surface, when the effects already noticed will 

 be produced, if carbolic acid is present. In carrying out this test, it 

 will, however, be found the most convenient to use a small white porce- 



1 Proceedings, Second Series, vol. ii., Science, p. 579. 



