390 



SCIENCE. 



[N. S. Vol. III. No. 63. 



explosion is enhanced by the inequality of 

 such mixtures. A flame spreading from a 

 spot rich in gas would propagate itself ex- 

 plosively through a mixture very poor in 

 gas. 



The danger is enhanced in the case of 

 acetylene by the low temperature at which 

 it takes fire, 480° Cent. Most other gases 

 must be treated to about 600° to take fire 

 and marsh gas, the fire damp of mines, 

 fortunately requires a much higher tempera- 

 ture to ignite, so that a spark from flint and 

 steel does not sufiice to cause an explosion. 

 Acetylene burns with greatest increase of 

 volume when the products are carbonic 

 oxide and hydrogen. The violence of com- 

 bination of acetylene with oxygen can be 

 well shown by igniting equal volumes of 

 the two gases. A quantity equal to 3-4 

 grains makes a far louder report than the 

 same weight of powder or of nitro-glycerine. 



The dangerous properties shown by acety- 

 lene need not condemn it, but particular 

 care must be taken to prevent leakage if 

 acetylene gas comes into use; fortunately 

 small pipes can be used and the gas con- 

 tains no ammonia, which, in common gas, 

 destroys the grease on the stopcocks and 

 promotes leakage. 



If instead of igniting a mixture of air and 

 acetylene, the latter alone is passed through 

 a glass tube heated to dull redness, at first 

 a slight change takes place, and liquid ben- 

 zene and other products condense in the 

 colder parts of the tube; at a little higher 

 temperature the change goes further — car- 

 bon is deposited and hydrogen is set free. 

 If the interior of the tube is carefully 

 watched it will be seen that the decomposi- 

 tion takes place with a dull red flame, as if 

 the acetylene were burning with an insuffi- 

 cient supply of air. N'o air, however, is in 

 the tube; there is no combustion in the or- 

 dinary use of the word, and yet we have in 

 the flame evidence of a sudden disengage- 

 ment of heat. Here we approach the solu- 



tion of the problem, regarding the extraor- 

 dinary chemical activity of acetylene. 

 Acetylene has a supply of heat stored up, 

 which it gives off, whenever it is decom- 

 posed spontaneously, burnt in air, or ex- 

 cited by any radical chemical change. The 

 sudden evolution of heat manifests itself as 

 light, quickens combustion and promotes 

 all chemical action. 



The exact quantity of heat absorbed and 

 stored up by acetylene, when it is formed 

 by the union of carbon and hydrogen, can 

 be best measured by two experiments. 

 Firstly, burn exactly one cubic foot of 

 acetylene in a calorimetric apparatus, which 

 is merely a device for heating a given 

 weight of water without loss of heat, and 

 find that nearly nine pounds of water can 

 be heated from its freezing to its boiling 

 point. Or, if we take the thermal unit in 

 more general use we find that 407 kilo- 

 grams of water gain one degree Centigrade 

 in temperature from the heat given oflf by 

 burning one cubic foot of acetylene gas, 

 measured at 0° Cent, and 76 cm. barome- 

 ter. 



Secondly, take exactly the weights of car- 

 bon and hydrogen which correspond to the 

 weight of one cubic foot of acetylene and 

 burn them in the same way under a weighed 

 quantity of water. We shall find that ac- 

 cording as we take pure amorphous carbon 

 or diamonds we get a somewhat different 

 quantity of heat. "With amorphous carbon 

 and hydrogen 336.5 kilograms of water are 

 raised 1 degree Cent, in temperature. The 

 difference of heating power then between 

 acetylene gas and the same weight of car- 

 bon and hydrogen is 71 heat units. The 

 surplus energy stored up in the acetylene 

 and set free when it is burnt becomes evi- 

 dent and is measured, when we find that 

 the acetylene arrangement or combination 

 of carbon and hydrogen atoms is capable of 

 making the elements do more work, that is 

 to heat 71 kilograms more water than when 



