122 Prof. F. Clowes. An Apparatus for [June 18, 



Nickel, Nickel, 



25 per cent. 22 per cent. 



Density. Temp. Density. Temp. 



After heating, non-magnetisable 8' 15 15'1 16'5 



After cooling, magnetisable 7'99 14'5 7'96 15'6 



After heating again, non-magnetisable 8'15 18'0 8'12 18'2 



After cooling again, magnetisable 7'97 ' 22'0 7'95 21'8 



The rings were each .time cooled to from 100 C. to 110 C. by 

 carbonic acid arid ether in vacua. 



IV. ''An Apparatus for testing the Sensitiveness of Safety- 

 lamps." By FRANK CLOWES, D.Sc., Lond, Professor of 

 Chemistry, University College, Nottingham. Communicated 

 by Professor ARMSTRONG, F.R.S. Received June 4, 1891. 



It is generally acknowledged that the Davy safety-lamp cannot 

 with certainty detect less than 3 per cent, of firedamp in the air of 

 the mine. Gas-indicators of much greater sensitiveness have been 

 invented ; amongt these the electrical apparatus of Liveing and the 

 spirit safety-lamp of Pieler take first rank. The objection to these 

 special forms is, however, a serious one. They do not serve for 

 illuminating purposes, and therefore it becomes necessary to carry an 

 ordinary safety-lamp, together with the testing apparatus. Many 

 attempts have been made to obviate this inconvenience by producing 

 a safety-lamp which shall serve the double purpose of illumination 

 and of detecting minute percentages of firedamp. The discovery of 

 such a lamp would be of great value to the miner, in view of the fact 

 that very low percentages of firedamp have been proved to be dan- 

 gerous in the presence of coal-dust. 



The following apparatus has been devised to render easy the process 

 of testing the sensitiveness of different forms of safety-lamps when 

 used for detecting firedamp. To enable satisfactory tests to be made 

 in the laboratory, it was necessary to insure (1) the easy and rapid 

 production of mixtures of firedamp and air in known proportions ; 

 (2) to insure economy of the artificially prepared methane, which 

 represented firedamp; and (3) to examine the flame of the lamp 

 under conditions as satisfactory as those existing in the mine. 



A wooden cubical box of about 100 litres capacity was constructed 

 so as to be as nearly gas-tight as possible. It was then made abso- 

 lutely gas-tight by painting it over with melted paraffin wax, which 

 was afterwards caused to penetrate more perfectly by passing an 

 ordinary hot flat-iron over the surface. This testing chamber was 

 furnished with a small inlet tube at tie top, and with a similar outlet 



