O0O ACTION OF HEAT MODIFIED 



Animal matter , " In scverd of these experiments, I found, wlien the pre- 

 *°Ted^under *^^"^ was not great, when equal, for instance, only to 80 at- 

 compression, mospheres, that the horn employed was dissipated entirely, the 

 7^^hayT\elt ^^^'^^ ^'^^^ which had contained it being left almost clean : yet 

 acoak. undoubtedly, if exposed to heat without compression, and pro- 



tected from the contact of the atmosphere, the horn would 

 leave a cinder or coak behind it, of matter wholly devoid of 

 Watility. Here, then, it would seem as if the moderate pres- 

 sure, by keeping the elements of the substance together, had 

 promoted the general volatility, without being strong enough to 

 resist that expansive force, and thus, that the whole had escap- 

 ed. This result, which I should certainly not have foreseen in 

 theory, may perhaps account for the absence o(coal in situa- 

 tions where its presence might be expected on principles of ge- 

 neral analogy." 



Since this publication, a very natural question has been put 

 to me. When the inflammable substance has lost weight, or 

 when the whole has been dissipated, in these experiments, 

 what has become of the matter thus driven oft'? 

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

 Tl e'matter™'^ ° fidence, more experiments are required. But, in the course 

 volatilized un- of practice^ two circumstances have occurred as likely, in 

 er pressure, ^lost cases, to have occasioned the loss alluded to. T 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 stinkstone. I conceive, that the 

 most volatile part of the horn has 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 full of horn, entirely empty after 

 the experiment, I was induced, as above stated, to conceive, 

 that, under pressure, it had acquired a greater general volati- 

 lity than it had in freedom ; and I find that, in the open fire, 

 horn yields a charcoal equal to 20 per cent, of the originAi 

 w<>ighti • But more experiments must be made on this 

 subject, 



Aiiother 



