568 Meeting of the British Association. [Oct., 



Mr. Graham, that gases diffuse in the inverse proportion to the 

 square root of their densities, or, more popularly, that light gases 

 diffuse more rapidly than heavy ones. Mr. Ansell showed, by ex- 

 periment, that when a tube closed at one end by plaster of Paris, 

 was filled with common coal gas, the lighter part of the compound 

 was rapidly diffused through the plaster, as was at once seen by the 

 yellow flame and slight explosion which ensued on bringing a lighted 

 match close to the closed end. Hence, Mr. Ansell said, his propo- 

 sition. In a pit the case is the reverse of that of the tube. There 

 the gas is ready to escape into the galleries, and the apparatus must 

 therefore be modified to suit the varying circumstances. The essen- 

 tial parts of the apparatus may be described as consisting of an alarm 

 bell and a telegraph needle — the former being rung and the latter 

 deflected by an electric current, which was set in motion by the 

 action of the dangerous gas. The means by which this was effected 

 consisted of an iron cup, on which was fixed a disc of white Sicilian 

 marble, standing on a U-tube, which contained a quantity of mer- 

 cury. The marble here represented the plaster which closed the 

 end of the tube in the first experiment, and through it the danger- 

 ous gas was diffused. As it did so, the mercury was pressed up 

 into the other extremity of the tube, completed the previously broken 

 circuit, and an alarm was given by the ringing of the bell and the 

 deflection of the needle. 



" Notes of Analyses of Gold Coins of Columbia, New Grenada, 

 Chili, and Bolivia, with some Account of the Operations of Gold 

 Mining in Nova Scotia," by George Lawson, Ph. D. The first part 

 of this paper was principally devoted to the history and description 

 of the gold coinage of the above-mentioned countries, with physical 

 and chemical analyses. Some information was then given respect- 

 ing the composition of the native gold of coining countries, and a 

 useful list was appended, showing the principal gold coins of various 

 countries, with their weights, fineness, and values, and a synopsis 

 of the results of assays and analyses of native gold from the chief 

 mines of the world. The author then proceeded to make some 

 remarks on the process lately invented by Mr. Crookes, by which 

 sodium amalgam is added to the mercury. He stated that he had 

 experimented to a considerable extent on the effects of sodium 

 amalgam, and found it to exert a very remarkable power in facili- 

 tating the absorption of gold by mercury, quite independently of 

 any action of the soda necessarily formed during the operation. 

 The coating of the copper surfaces with mercury alone had been 

 found practically to be a troublesome and tedious operation ; but the 

 use of a little sodium amalgam added to the mercury enabled the 

 coating to be given by a simple rubbing without any waste of time. 

 Some illustrations of the advantages of Mr. Crookes's process were 

 then given. It was stated that in some experiments undertaken in 



