Maech 13, 1896.] 



SCIENCE. 



389 



comparing other modes of lighting. It is 

 to be remarked that authorities differ widely 

 in their estimates, and the cost of gas and 

 electric lighting varies greatly with the lo- 

 cality. Electricity is particularly advantage- 

 ous when it can be put to other uses during 

 a part of the day. 



THE CHEMICAL PROPERTIES OF ACETYLENE. 



A series of very simple experiments will 

 illustrate the most important properties of 

 acetylene. 



To compare its density and its explosive 

 force with those of common gas take two 

 lamp chimneys closed at the top and bottom 

 with corks, and each fitted with an inlet 

 tube at the bottom and with a large brass 

 tube at the top. Fill one with gas and the 

 other with acetylene and light both gases at 

 the upper tube ; then remove the rubber 

 tubes from the inlet tubes. The flames 

 will continue to burn at the upper orifice, 

 because each gas rises, floating on a layer 

 of air, which rushes in from below, and the 

 relative densities of the gases may be esti- 

 mated from the rapidity with which each 

 flows out. The common gas flows out more 

 rapidly and burns with a higher flame than 

 the acetylene, because it is lighter: (density 

 of Boston gas=0. 607 ; density of acetylene 

 =0.91). At the last the flame strikes 

 down into the small residue of each gas, 

 which has become mixed with air in^ the 

 lamp chimneys, and a slight explosion takes 



place, which is notably stronger with acety- 

 lene than with gas. The greater density of 

 acetylene explains partly why it should 

 have more illuminating power than com- 

 mon gas, since a cubic foot contains more 

 material. As our object is only to examine 

 the properties of acetylene which have a 

 bearing upon its illuminating power, one 

 test of its chemical activity will sufiice. Set 

 free a small quantity of hypochlorous acid 

 gas in a tall glass jar and plunge into it a 

 tube from which a stream of acetylene is 

 issuing, this latter will immediately take 

 fire from the great heat evolved by its 

 chemical action upon the hypochlorous acid. 

 If common gas, or almost any other gas, 

 were subjected to the same test no flame 

 would result. 



Acetylene forms peculiar salts with cop- 

 per, silver and mercury ; and these when 

 dry decompose explosively when subjected 

 to a shock or to the action of heat. The 

 silver compound can even be exploded 

 under water and is more dangerous than 

 fulminate of silver. 



EXPLOSIVENESS OF ACETYLENE. 



What we have learned concerning the 

 extreme chemical activity of acetylene leads 

 us to expect that it would form more readily 

 than other gases an explosive mixture with 

 air, and this proves to be the case. 



Experiments using a piece of two-inch 

 gas pipe as a cannon show that 5-6% of 

 acetylene mixed with air forms an explosive 

 mixture ; 10-12 % of water gas is required 

 to explode with air. 



The heat abstracted by the walls of the 

 iron tube prevents the mixture from obtain- 

 ing its limit of explosiveness, and a still 

 smaller percentage of either gas mixed with 

 the air of a room would explode. Lechat- 

 elier (Comptes Eendus, 1895, II., 1145) 

 gives 2.8% of acetylene mixed with air as 

 the explosive limit, and it is to be noticed 

 that in a dwelling house the danger from 



