Detection of AJulterations. 7 ! 



ministering this acid, but have, as yet, only satisfied ourselves, that the 

 alcoholic solution is, for internal use, the best form.* In using the 

 acid which has been prepared by passing sulphuretted hydrogen gas 

 through a solution of cyanuret of mercury, care must be taken to 

 ascertain that the whole of the mercury has been precipitated ; as 

 we have known patients to be salivated by an acid containing a very 

 small proportion of mercury. The best mode of detecting the im- 

 purity consists in putting a few drops of the liquid upon a plate of 

 gold, and then placing a clean piece of zinc in contact with both gold 

 and acid ; if mercury be present, the gold will be whitened. Tin must 

 not be used in place of zinc. The comparative strength of any two 

 specimens may be ascertained by distiUing equal quantities of each, 

 from retorts into receivers containing a solution of nitrate of silver; by 

 which a white cyanuret of silver will be precipitated, every 1681.66 

 grains of which indicate 342.495 grains of pure acid. We would 

 suggest the propriety of adding some bits of iron to the acid, an 

 hour before the above process, in order to neutrahze any hydro- 

 chloric acid which might be present. If any portion of the precipi- 

 tate be insoluble in nitric acid, it may be considered as chloride of 

 silver. 



Alcohol. — The alcohol of commerce is contaminated by coloring 

 matter and water, from which it may be purified by exposure to sub- 

 stances having a strong affinity for Vi^ater, and subsequent distillation. 

 When distilled from acetate of potash or chloride of calcium, it con- 

 tains a small quantity of ether; which, however, does not impair its 

 medicinal properties. Neither is it injured by the minute quantity of 

 oil which it often contains, and which varies with the vegetables from 

 which the spirit has been obtained. The quantity of water contain- 

 ed in the alcohol of commerce, or in any specimen of dilute alcohol, 

 may be easily determined with sufficient accuracy for pharmaceuti- 

 cal purposes. Put into a bottle 100 drachm measures of the fluid, 

 and add small lumps of dry carbonate of potash (pearlash) until they 

 cease to dissolve; after some hours pour off the alcohol, and meas- 

 ure it accurately. Its volume, subtracted from the original measure, 

 will indicate the quantity of water. The specific gravity of alcohol 

 which has been freed from solid matter by distillation, is a still more 



* We have exposed a dilute solution of this acid in concentrated alcohol (o the 

 direct beams of the sun, for many hours, without any change of color or other evi- 

 dence of dccom position. 



