Chemistry. 175 



Many reagents decompose tartar emetic, and cause precipitates in its 

 solution. Of these the principal are alkaline substances, the stronger acids, 

 such as the muriatic and sulphuric, the infusion of gall-nuts, and sulphu- 

 retted hydrogen. The value of these tests is very unequal. Pure potash, 

 when cautiously added to a strong solution of tartar emetic, occasions a 

 pretty copious flocculent white precipitate, which is readily and completely 

 redissolved by an excess of the alkali. In a moderately dilute solution 

 potash does not produce any change. Pure ammonia in a concentrated 

 solution throws down a white, very fine, granular precipitate, which ad- 

 heres firmly to the glass, and is only partially redissolved by an excess of 

 the precipitant. Tartar emetic is not precipitated by carbonate of ammonia. 

 The fixed alkaline carbonates and lime water act with considerable delica- 

 cy. In a solution containing a grain of tartar emetic to an ounce of dis- 

 tilled water, carbonate of potash and lime water yield distinct white pre- 

 cipitates, that from the former being the protoxide of antimony with a 

 little carbonic acid, and that from the latter consisting of the tartrates of 

 antimony and lime; whereas in the same liquid pure potash produces no 

 change, and ammonia a cloudiness scarcely visible. When the tartar eme- 

 tic is in the proportion of one grain to two ounces of water, lime-water has 

 no effect, but the carbonate of potash still gives rise to a precipitate. If 

 the proportion is a grain to four ounces of water, the action of the alkali 

 can no longer be traced. 



The delicacy of muriatic or sulphuric acid as a test of tartar emetic, is 

 almost exactly the same as that of the carbonate of potash ; but the acid 

 must be added cautiously, as an excess of it redissolves the precipitate. >' 



The recent infusion of gall-nuts produces a copious yellowish white pre4 

 cipitate in a concentrated solution of tartar emetic. The liquid is render- 

 ed turbid, when the proportion is two grains to an ounce ; but it under- 

 goes no change when the tartar emetic is in the ratio of one grain to an 

 ounce of water. 



Sulphuretted hydrogen acts with far greater delicacy and certainty than 

 any of the others. On transmitting this gas through eight ounces of water 

 containing one grain of tartar emetic, the solution instantly acquired an 

 orange colour ; and after saturating the liquid with the gas, and boiling 

 in order to expel the excess of it, a considerable quantity of the sulphuret 

 of antimony quickly separated. * 



From these experiments it fully appears, that of all the tests of tartar 

 emetic enumerated by toxicologists, sulphuretted hydrogen is the only one 

 which is sufficiently delicate for being entitled to confidence. It is the 

 only one, also, the indications of which as to the presence of antimony are 

 precise. The orange tint'of the precipitated sulphuret of antimony can 

 scarcely be mistaken for any other metallic sulphuret by a person acquaint- 

 ed with its appearance. Its colour is quite different from that of orpiment 



* This precipitate is commonly, but I conceive incorrectly, regarded as a hydro- 

 sulphur ct of the oxide of antimony. It appears rather to be a hydrated sulphuret 

 of the metal. 



