■gSo Dr. Fordyce on the Cause of the additional Weight 
ftom 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, until it came away as pure as when 
applied, to all sensible trials. The quantity of water used was 
above four pounds. I evaporated this water to dryness, and 
heated the mass red hot, to expel the whole of the water; it 
weighed seven grains more than the vitriolated tartar procured 
from applying the acid and alkali as above. After evaporating 
the water, I dissolved the mass again in 40 ounces Troy weight 
of pure water ; a yellowish powder separated. The solution 
of the vitriolated tartar, cleared of this powder, was again eva- 
porated to dryness, and the water of crystallization driven 
off. It now weighed 976-5— grains, which is nearly two 
grains less than the vitriolated tartar I obtained from the acid 
and alkali applied simply together, without the intervention 
of the zinc. 
The vitriolated tartar now obtained was free from any mix- 
ture. The additional weight of the calx of the zinc did not arise, 
therefore, from either the acid or the alkali : it remains, there- 
fore, that it arose from the water. 
The weight of the calx of the zinc was ascertained by dry- 
ing it after washing out the vitriolated tartar, heating it to a 
red heat, and afterwards weighing it. The weight of the 
zinc dissolved in saturating the acid, was 164 grains : the weight 
of the calx 220 grains. The additional weight was, therefore, 
56 grains. 
