Effects of Heat modified hj Gornpremdm ' i.i 



almost clean ; yet undoubtedly,- if exposed to beat •■ >ut 

 compression, and protected from the contact of the atmo- 

 sphere, the horn would leave a cinder or coke behind it, of 

 matter wholly devoid of volatility. Here, then, it would 

 seem as if the moderate pressure, by keeping the elements 

 of the substance together, had promoted the general vola- 

 tility, without being strong enough to resist that expansive 

 force, and thus, that the whole had escaped. This result, 

 which I should certainlv not have foreseen in theory, may, 

 perhaps, account for the absence of coal in situations where 

 its presence might be expected on principles of general ana- 

 logs'." 



Since this publication, a very natural question has been 

 put to me. When t tie inflammable substance has lost 

 weight, or when the whole has been dissipated in these ex- 

 periments, what has become of the matter thus driven off ? 



I must own, that to answer this question with perfect con- 

 fidence, more experiments are required. But, in the course 

 of practice, two circumstances have occurred as likely, in 

 most cases, to have occasioned the loss alluded to. I found 

 in these experiments, particularly with horn, that the chalk, 

 both in powder and in lump, which was used to fill vacuities 

 in the tubes, and to fix them in the cradle, was strongly im- 

 pregnated with an oily or bituminous matter, giving to the 

 substance the qualities of a stinkstonc. I conceive that the 

 most volatile Dart of the horn ha* been conveyed to the 

 chalk, partly in a state of vapour, and partly by boiling over 

 the lips of the glass tube, the whole having been evidently 

 in a state of very thin fluidity. Having, in some cases, found 

 the tube, which had been introduced lull of horn, entirely 

 empty after the experiment, I was induced, as above stated, 

 to conceive, that, under pressure, it had acquired a greater 

 general volatility than it had iu freedom; and 1 find that, in 

 the open fire, horn yields a charcoal equal to £0 per cent. 

 of the original weight. But more experiments must be u idc 

 on this subject. 



Another cause of the loss of weight lay undoubtedly in 

 the excess of heat employed in most of them to remove the 

 cradle from the barrel. With inflammable substances no 



air- 



