Chemistry and Mineralogy. 395 



of these Colonel Robinson discovered a large quantity of carbo- 

 nate of magnesia. Dr Daubeny found a quantity coating the 

 upper surface of the lava. Dr Dalton observed, that there 

 could be no doubt as to the subhmation of carbonate of magne- 

 sia, as Dr Henry had informed him that a quantity of this salt 

 was always driven off whenever the heat was carried beyond a 

 certain height. 



10. Dr Dalton stated the results of his examination of the 

 spirit distilled from caoutchouc. He found it to depress the ba- 

 rometer like sulphuric ether. It passes through water without 

 diminishing its volume, thus differing from ether. It is ab- 

 sorbed by water like olefiant gas. It consists of 2 olefiant gas. 

 10 volumes when burned give 40 carbonic acid, and require 60 of 

 oxygen. It appears to be the same as a substance described by 

 Faraday. It differs from coal-gas in this, that the latter con- 

 sists of double olefiant gas. The observations of Mr Davy up- 

 on this subject corresponded with those of Dr Dalton, 



Wednesday, I2th August. — 11. Mr Mallet described the 

 phenomena presented in lamps, when the holes for the passage 

 of the gas are made as small as possible, and also the appear- 

 ance observed when the direction of the tube is inclined in dif- 

 ferent ways, two currents being formed when the tube is in- 

 chned, and the surface of the flame presenting spiral lines, and 

 considerable retraction of the flame taking place, none, however, 

 occurring when the tube is not fully inserted. The apertures 

 in the lamp were less than the ^l^ of an inch in diameter. In 

 the discussion which arose from this communication, Dr Dalton 

 observed, that twelve small holes in a lamp consumed less gas 

 and gave more heat, than when the holes were larger but fewer 

 in number. But the great object in procuring a proper quanti- 

 ty of heat depends upon the atmospheric air being neither too 

 great nor too small in quantity. He stated, that if we take a 

 cubic inch of pure gas, and another diluted with half its volume 

 of air, each gives out the same quantity of heat, but the latter 

 scarcely yields any light. This is an important fact, and de- 

 serves to be known. 



12. Mr Connell read a paper, in which it was his object to 

 point out some chemical facts, by which we may be enabled to 



