Davy — On a Kew Chemical Test for Alcohol. 579 



XLIX. — Ox A Xew Chemicax Test eor Alcohol. Ey ED^irtn) W. 

 Davy, A.M., M.D., Professor of Forensic Aledicine, Eoyal College 

 of Sui'geons, Ireland, &c. 



[Read May 22, 1876.] 



"W^HTLST making lately some experiments on molybdic acid, I observed 

 that when a solution of that substance in strong sulphuric acid was 

 brought in contact with alcohol, there is very quickly developed a 

 deep azure blue colouration ; and this fact, being (as far as I was able 

 to ascertain) hitherto uni'ecorded, led me to investigate the reaction to 

 determine the cause of this production of colour. 



As I found that the protosulphate of ii'on, and the protochloride 

 of tin, two powerful deoxidizing salts, produced a similar effect on 

 this solution, there was but little doubt that it was due to the deoxi- 

 dizing action of alcohol on the molybdic acid. And I afterwards 

 found that the blue substance which was formed in the case of alcohol 

 possessed all the characters of the blue compound which is produced 

 when molybdic acid or its salts are acted on by different reducing 

 agents, whereby a substance consisting of five atoms of the metal 

 molybdenum with fourteen of oxygen is obtained, which is usually 

 regarded as a combination of the binoxide of molybdenum with molyb- 

 dic acid, the following formula (MoOo, 4 M0O3) representing its 

 composition. 



With certain precautions wliich I shall presently point out, I have 

 found that this reaction of alcohol on the molybdic solution stated is 

 extrem'.ily sensitive, so that by its indications very minute quantities 

 of alcohol, even when diluted with large proportions of water, may be 

 readily detected. Thus, for example, if one part by volume of com- 

 mercial rectified spirits be mixed with a hundred parts of distilled 

 water, and one small di'op of this mixture be taken, the minute 

 quaniic} of spirit contained in it can be easily detected by the deep 

 blue colouration which will be immediately developed on bringing it 

 into contact with the molybdic solution, employed in the manner about 

 to be described. But this is not the limit of the delicacy of this test, 

 for I have been able by means of it to detect the spirit in one drop of 

 a mixture of distilled water and anhydrous spiiit, in which the latter 

 substance constituted only the one-thousandth part of its volume ; 

 and as the drop was found to weigh six-tenths of a grain, the quantity 

 of real or auhydious alcohol contained in it would be less than the one- 

 sixteen hundred and sixty-sixth part of a grain of that substance. 



Though small quantities of spirit, even when considerably diluted 

 with water, will produce with the molybdic solution the blue reaction 

 without the assistance of any external heat, still where very minute 

 quantities, diluted with such large proportions of water as those just 

 stated, are to be detected, it is necessary for the success of the experi- 

 ment that the reaction should be assisted by a gentle heat, and also 



