468 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ing body. These instruments are, first, the reed trumpet, the 

 air being condensed by a caloric engine ; second, the siren 

 trumpet, the revolving disk being driven by steam from a 

 high-pressure boiler; third, the ordinary locomotive whistle 

 blown by steam from a high-pressure boiler. Proc. Nat. 

 Acad., N. Y. Tribune, October 31, 1873. 



SAWDUST AS FUEL. 



The expense of forming sawdust into compact blocks, in 

 which, like turf, tan, etc., it is best adapted for fuel, leads many 

 to be satisfied with smaller heating results in burning it in a 

 loose condition. A much better effect may, however, be ob- 

 tained under such circumstances by adding about one sixth 

 their weight of mineral coal : the high temperature produced 

 by the combustion of the latter causing a more rapid expul- 

 sion of the 25 to 40 per cent, of moisture present in the saw- 

 dust, as well as a more rapid development and more complete 

 combustion of inflammable gases. For the best effect, how- 

 ever, a peculiar grate is necessary. 6 C\ January 8, 1874, 

 18. 



EXPLOSION OF GUN-COTTON". 



For a long time Professor Abel, at Woolwich, has been con- 

 ducting experiments upon gun-cotton ; and very lately he has 

 obtained results of unusual interest. In the first place, he 

 finds that the explosion of gun-cotton is, so to speak, sympa- 

 thetic, varying according to the manner in which it is begun. 

 If, in the form of yarn, the gun-cotton be ignited by a spark, 

 it smoulders slowly away ; a flame causes it to burn rapidly ; 

 fired as a charge, it behaves with corresponding vigor; and 

 exploded by a fulminating powder, it acts with tremendous 

 violence. Every fulminating powder, however, will not ex- 

 plode gun-cotton, it seeming to need a peculiar set of vibra- 

 tions to which alone it will respond. Fulminating mercury, 

 the ordinary powder of percussion-caps, seems the best agent 

 for this purpose. If gun-cotton, compressed into cakes, be 

 arranged in a line, and a cake at one end detonated by the 

 fulminate, the detonations follow each other along the line 

 with marvelous velocitv a velocitv, according to the electric 

 chronoscope, of about 20,000 feet, or nearly four miles per 

 second. When we recollect that a rifle-bullet usually travels 



