which Metals acquire by being calcined. 377 
of the metal, shews that there is a substance added to the whole 
metal ; or, that while some substance is driven off, another is 
added in greater quantity ; since it is clear, from various ex- 
periments well known to this learned body, that all matter 
gravitates, and that all the substances found in this earth, which 
have been tried, gravitate equally. This additional matter 
must be added to the metal either from the acid, the alkali, 
the water used in the solution, the air lying on the surface of 
the materials during the time of the operation, or it must come 
through the vessels in which the operation is performed. To 
ascertain this, I made the following experiment. 
I took a large quantity of vitriolic acid, purified by distilla- 
tion (about two pounds, it not being material what quantity 
was taken exactly), I diluted it with distilled water about four 
or five times its weight by guess (the exact proportion being 
also immaterial), I applied to 1000 grains of this diluted acid 
a sufficient quantity for saturation of aqua kali puri, of the 
London Dispensatory, rendered pure from fixed air, as is pre- 
scribed in the process of the College ; I poured in the aqua 
kali puri to the diluted acid, by a little at a time, until it was 
nearly saturated. I then poured in some juice of violets, which 
gave the whole a red colour. I continued to add aqua kali puri, 
by a little at a time, until the red colour just disappeared. I 
added the aqua kali puri to the acid, rather than the acid to 
the alkali, because the loss of the red colour at the point of sa- 
turation can be discerned much better than the loss of the yel- 
low colour, which the alkali intermixes with the natural blue. 
I ascertained the weight of the aqua kali puri, by weighing 
the bottle containing it before any was poured into the acid* 
