106 ESSAY VI. 



receiver. The receiver is then to be applied again, but not 

 luted. The mixture soon begins to foam, and volatile red 

 nitrous acid goes over. Meanwhile the distillation is to be 

 continued till no more red vapours appear^ when again 1 oz. 

 of finely powdered arsenic is to be added, the receiver applied 

 as before, and a gentle ebullition continued, till this be like- 

 wise dissolved; and afterwards 1J oz. of nitrous acid is to 

 be added, whereupon a new effervescence and red vapours 

 will arise ; the recipient is to be applied, and the whole 

 distilled to dryness ; there will remain a white mass; 

 and, lastly, the fire is to be increased so far as to make this 

 mass thoroughly red hot. The acid obtained in the receiver 

 during the operation may serve for the same purpose several 

 times. After the retort has grown cold, it is to be broken, 

 and the white mass is to be put into a closed vessel, with 

 this signature, Dry acid of arsenic ; or if you please you may 

 reduce it to coarse powder in a glass mortar, put it into a 

 glass retort, pouring a double quantity of distilled water upon 

 it, apply a receiver, and boil it for a few minutes till the 

 acid is dissolved ; the water that goes over is to be poured 

 back into the retort. The solution is then to be filtered 

 through blotting paper, which has been previously washed in 

 hot water, and then to be preserved in a phial with a glass 

 stopple, under the name of Liquid acid of arsenic. 



It is to be observed that arsenic must necessarily be 

 deprived of its phlogiston before the acid can be obtained ; 

 this is principally effected by the nitrous acid. It may seem 

 as if it should be sufficient to distil the nitrous acid from 

 the arsenic, after which the acid of arsenic would remain 

 behind ; but in this manner only a very small portion of 

 arsenic will be decompounded ; for this salt requires first to 

 be dissolved in water, in order that the nitrous acid may act 

 upon it in all its points ; but nitrous acid dissolves only a 



