March 13, 1896.] 



SGIENGE. 



391 



the same elements are free in the state of 

 amorphous carbon and of hydrogen gas. 



When the carbon from carbide of calcium 

 and hydrogen from water combine to make 

 acetylene heat is utilized in changing the 

 carbon from the solid and the hydrogen 

 from the liquid form to the form of a gas. 

 Heat is absorbed in this process which im- 

 parts a new energy of motion to the atoms, 

 in the same way that heating water sepa- 

 rates the particles to two thousand times 

 wider distances from each other and gives 

 them the energy of motion which is appar- 

 ent in steam. In this case we can measure 

 the amount of heat required for this work 

 and which is absorbed while it takes place. 

 Unfortunately we can not get similar meas- 

 ures with carbon vapor and solid carbon, 

 and we can only measure a total absorp- 

 tion of heat during the generation of acetj'- 

 lene, and we suppose that the total, 71 heat 

 units, may be made up by the absorption of 

 a larger amount of heat in order to change 

 amorphous carbon to the gaseous state, from 

 which must be deducted the heat which is 

 given out when two carbon and two hydro- 

 gen atoms combine to make C2H2. Ben- 

 zene which has exactly the same percentage 

 of carbon and hydrogen, but combined into 

 quite a different chemical group shows that 

 more energy has been expended in bringing 

 about its chemical arrangement. The signs 

 which attest this are greater stability, 

 smaller chemical activity, and above all the 

 fact that when benzene is burnt it gives off 

 much less heat than the same weight of 

 acetylene does, and in fact only 4 heat units 

 more than the same weight of carbon and 

 of hydrogen. 



It has seemed necessary to explain fully 

 how quantities of energy, which can usually 

 be measured in terms of heat, preside over 

 the making of different chemical compounds, 

 and how the dormant heat can be made ac- 

 tive again when the compounds are excited 

 to chemical change, and how each one is 



stamped as with a birth mark by its special 

 heat value. 



This peculiar stamp set upon acetylene is 

 at the same time a token of valuable and 

 also of dangerous qualities. Heat is added 

 to the heat of combustion and brings about 

 more sudden changes and places acetylene 

 with the class of bodies known as fulmi- 

 nates. These are distinguished from ex- 

 plosives like gunpowder by their capability 

 of suddenly evolving stored-up heat, which 

 causes a great expansion of gaseous prod- 

 ucts. Berthelot has calculated that ful- 

 minate of silver develops a pressure of 600,- 

 000 lbs to the square inch in the incredibly 

 short time of one-thirty-millionth of a sec- 

 ond. The acetylide of silver has similar 

 properties, and the lightest shock suffices to 

 explode it. It occurred to Berthelot to see 

 whether acetylene gas might not decompose 

 spontaneously into carbon and hydrogen 

 with explosive suddenness. We have seen 

 that it decomposes into these products, hut 

 without explosion, when strongly heated, and 

 only in one way could it be made to decom- 

 pose explosivelj^. Berthelot succeeded in 

 detonating pure acetylene by subjecting it 

 to the shock of fulminate of silver. 



The danger seems very slight that acety- 

 lide of copper or some other metal may 

 form in an acetylene gas-holder, and when 

 exploded by friction or heat cause the 

 whole mass of gas or liquid acetylene to ex- 

 plode. The subject, however, is worthy of 

 further study. 



As was said in the beginning, the prob- 

 lems which are suggested by this new in- 

 dustry touch on all sides upon some of the 

 most important of the recent discoveries in 

 chemistry and physics, and the ease with 

 which acetylene can be obtained opens the 

 door to many new experiments. Such ques- 

 tions, for instance, as the use of acetylene in 

 gas engines, under special conditions, where 

 the high price would not be prohibitive, 

 would offer a very interesting study. It 



