126 EFFECTS of HEAT 
I found, that chalk expofed to a heat above that of boiling 
water, but quite fhort of rednefs, loft 0.34 per cent.; and in 
another fimilar trial, 0.46 per cent. Now, this lofs of weight 
equals within o.o1 per cent. the lofs in the laft-mentioned ex- 
periment, that being 0.47; and far furpafles that of the laft 
but one, which was but 0.074. There is good reafon, there- 
fore, to believe, that had the carbonate, in thefe two laft ex- 
periments, been previoufly dried, it would have been found 
during compreflion to have undergone no lofs. 
Tue refult of many of the experiments lately mentioned, 
feems fully to explain the perplexing difcordance between my 
experiments with porcelain tubes, and thofe made in barrels of 
iron. With the procelain tubes, I never could fucceed in a 
_ heat above 28°, or even quite up toit; yet the refults were 
often excellent. Whereas, the iron-barrels have currently 
ftood firm in heats of 41° or 51°, and have reached even to 
70° or 80° without injury. At the fame time, the refults, 
even in thofe high heats, were often inferior, in point of fu- 
fion, to thofe obtained by low heats in porcelain. The rea- 
fon of this now plainly appears. In the iron-barrels it has 
always been confidered as neceffary to ufe an air-tube, in con- 
fequence of which, fome of the carbonic acid has been fe- 
parated from the earthy bafis by internal calcination : what 
carbonic acid remained, has been more forcibly attracted, ac- 
cording to M. BERTHOLLET’s principle, and, of courfe, more 
eafily comprefled, than when of quantity fufficient to faturate 
the lime: but, owing to the diminished quantity of the acid, 
the compound has become leis fufible than in the natural 
ftate, and, of courfe, has undergone a higher heat with lets 
effe@. The introduction of water, by furnifhing a reacting 
force, has produced a ftate of things fimilar to that in the 
porcelain tubes ; the carbonate fuftaining little or no lofs of 
weight, 
