MODIFIED by COMPRESSION, 141 



It was eflential, in this mode of operation, that the whole 

 of the metal mould continue in a liquid Hate during the adion 

 of heat ; but when I was fatisfied as to its intensity and dura- 

 tion, I congealed the metal, either by extinguifhing the furnace 

 entirely, or by pouring water on the barrel. As foon as the 

 heat began to act, drops of metal were feen to force themfelves- 

 between the barrel and the leather, following each other with 

 more or lefs rapidity, according to circumftances. In fome 

 experiments, there was little exudation; but few of them 

 were entirely free from it. To fave the metal thus extruded^ 

 I placed a black-lead crucible, having its bottom perforated, 

 round the barrel, and. luted clofe to it, (fig. 37.) ; fome fand 

 being laid in this crucible, the metal was collected on its fur- 

 face. On fome occafions, a found of ebullition was heard 

 during the action of heat; but this was a certain fign of fail- 

 ure. 



The remits of the molt important of thefe experiments, 

 have been reduced to a common ftandard in the fecond table 

 placed in the Appendix ; to which reference is made by the 

 following numbers. 



No. 1. — On the 16th of June 1803, I made an experiments 

 with thefe arrangements. I had tried to ufe a weight of 30 lb.. 

 producing a preflure of 90 lb., but. I found this not fiifEcient. 

 I then hung on a. weight of 1 cwt., or 112.1b. ; by which a com- 

 prefling force was applied of 3 cwt. or 3361b. Very little 

 metal was feen to efcape, and no found of ebullition was heard. 

 The chalk in the body of the large tube was- reduced to quick- 

 lime ; but what lay in the inner tube was pretty firm, and ef- 

 fervefced to the lafl. One or two facettes, of good appearance, 

 were likewife found.. The contents of the fmall tube had loft, 

 but 2.6 per cent. j but there was a fmall vifible intrufion of me- 

 tal, and the refult, by its appearance, indicated a greater lofs. 

 I confidered.this, however, as one point gained; that being the 



firil: 



