MODIFIED ly. COMPRESSION. 117 
four experiments ‘differ from each other only in the abe em- 
ployed, and:in the: ‘quantity of air introduced, 
Tue firft of thefe experiments was, made on the 27th of A- 
pril 1893, in oneiof the large barrels, of old fable, with all the 
’ above-mentioned arrangements. The heat had rifen, contrary 
to my imtention, to 78° and 79°. The tubes came out un- 
* contaminated with fufible metal, and every thing bore the ap- 
‘pearance of foundnefs. The contents of the little tube, con- 
- fifting of pounded chalk, and of a fmall piece of lump-chalk, 
came out clean, and quite loofe, not having adhered to the 
infide of the tube in the fmalleft degree. There was a lofs of 
41 per cent., and the calcination feemed to be complete ; the 
fubftance, when thrown into nitric acid, turning red, without 
effervefcence at firft, though, after lying a few minutes, fome 
bubbles appeared. _According to the method foltowed in all 
thefe experiments, and. lately defcribed at length, (and fhewn 
in fig. 24. & 25.), the large tube was filled. over the fmall one, 
with various mafles of chalk, fome in lump, and fome rammed 
into it in powder ; and in the cradle there lay fome pieces of 
chalk, filling up the fpace, fo that in the cradle there was a 
continued chain of carbonate of four or five inches in length. 
The fubftance was found to be lefs and lefs calcined, the more 
it was remoyed from the breech of the barrel, where the heat 
was greateft. ~A fmall piece of chalk, placed at the diftance 
of half an inch from the fmall tube, had fome faline fubftance 
in the heart, furrounded and intermixed with quicklime, dif- 
tinguifhed by its dull white. In nitric acid, this fubftance be- 
came red, but effervefced pretty brifkly; the effervefcence 
continuing till the whole was diflolved. The next portion 
of chalk, was in a firm ftate of limeftone ; and a lump of 
chalk in the cradle, was equal in perfedtion to any marble 
_ [ have obtained by compreffion: the two laft-mentioned pieces 
of chalk efferyefcing with violence in the acid, and fhewing 
no 
