Effects of Heat modified hj Compression. J 3 



out with more suddenness and violence than in anv former 

 experiment; but the rod remained in its place, beino- secured, 

 bvacord. The upper pyrometer gave 27°, the lo;ver 23 n . 

 The contents of the inner tube had lost 1*8 per cent. The 

 upper end of the little lump of chalk was rounded and glazed 

 by fusion; and the letter which I have been in the habit of 

 cutting on these small pieces, in order to trace the degree of 

 action upon them, was thus quite obliterated. Or. the lower 

 end of the same lump, the letter is still risible. Both the 

 lump and the rammed chalk were in. a good semi-transparent 

 state, shining a little in the fracture, but with no good f'a- 

 cettes, and no where appearing to have acted on the tube. 

 This lait circumstance is of consequence, since it seems to 

 show, that this very remarkable action of heat, under com- 

 )ii, was performed without the assistance of the sub- 



. ice of the tube, by which, in many other experiments, 

 a considerable additional fusibility has been communicated 

 to the carbonate. 



These experiments, and many others made about the same 

 time, with the same success, clearly prove the efficacy of 

 water in assisting the compression ; and results approaching 

 to these in quality, obtained, in some cases, by means of a 

 very small air-tube, show that the influence of water on this 

 occasion has been merely mechanical. 



During the following summer and autumn 1803, I was 

 occupied with a different branch of this subject, which I 

 shall soon have occasion to mention. 



In the early part of last year (1804) I again resumed the 

 sort of experiments lately described, having in view princi- 

 pally to accomplish absolute compression, in complete imi- 

 tation of the natural process. In this pursuit I did not con- 

 fine myself to water, but made use of various other volatile 

 substances in order to assist compression ; namely, carbo- 

 nate of ammonia, nitrate of ammonia, gunpowder, and 

 paper impregnated with nitre. With these I obtained some 

 good results, but none such as to induce me to prefer anv 

 of these Compressors to water. Indeed, 1 am convinced that 

 water is superior to them all. I found, in several experi- 

 . tents, nftde with a simple air-tube, without anv artiiicial 



compressor, 



