248 PHILOSOPHICAL TRANSACTIONS. [aNNO 1792. 



when part of tlie tube d being broken off, it was left to stand for 24 hours, to 

 allow the inflammable air remaining in the vessel to fly off, and give place to the 

 air of the atmosphere ; which happened spontaneously from the different specific 

 gravities of the 2 vapours. 



The vessel containing the solution of the zinc was now laid on its side, and 

 10148 grs. of aqua kali puri were introduced by a crooked funnel into the globe 

 B, being the quantity sufficient to saturate 1000 grs. of vitriolic acid, as before 

 determined. Then the tube d was hermetically sealed, and the whole weighed. 

 The vessel was then raised, so that the globe a was undermost ; this was done 

 very gradually, so that the aqua kali puri was gradually added to the solution of 

 the zinc : when a little was poured in, the vessel was brought into an horizontal 

 position again, and shaken a little; this was repeated till the whole of the aqua 

 kali puri was poured in. The zinc was thus precipitated in the form of a calx. 

 It was suffered to stand for 48 hours: no alteration of the gravity took place, 

 therefore nothing had entered through the glass to give additional weight to the 

 zinc in order to calcine it. 



The next step was to open the tube, which was done under water, and in an 

 atmosphere of the same heat in which it was sealed, viz. 57° of Fahrenheit's 

 thermometer. The air was neither diminished nor increased, none of the water 

 being driven into the apparatus by the weight of the atmosphere, and none being 

 thrown out. On heating the globe b, so as to drive out some of the air, it was 

 found to be of the same purity nearly as that of the atmosphere, being tried by 

 the application of nitrous air produced from solution of mercury. The weight 

 therefore which the calx had gained, arose neither from any substance passing- 

 through the glass, nor from the super-incumbent air during the precipitation. 

 It must therefore be either from the acid, the alkali, or the water. 



To determine whether the acid or alkali gave the weight to the calx of the zinc, 

 I washed out the kali vitriolatum, formed by the combination of the vitriolic 

 acid and the kali, with pure water, repeatedly applied, till it came away as pure 

 as when applied, to all sensible trials. The quantity of water used was above 

 4 lb. I evaporated this water to dryness, and heated the mass red-hot, to expel 

 the whole of the water ; it weighed 7 grs. more than the vitriolated tartar pro- 

 cured from applying the acid and alkali as above. After evaporating the water, 

 I dissolved the mass again in 40 oz. Troy weight of pure water ; a yellowish 

 powder separated. The solution of the vitriolated tartar, cleared of this powder, 

 was again evaporated to dryness, and the water of crystallization driven oft'. It 

 now weighed 976-rV grs., which is nearly 2 grs. less than the vitriolated tartar 

 obtained from the acid and alkali applied simply together, without the interven- 

 tion of the zinc. The vitriolated tartar now obtained was free from any 

 mixture. The additional weight of the calx of the zinc did not arise there- 



