SCIENTIFIC NOTES. 



41 



acids, after which it is again shredded, boiled to remove dangerous 

 impurities, subjected to hydraulic pressure to remove excess of 

 v^rater, and moulded into suitable forms for shipping and use. Until 

 about sixty years ago the only explosive known for all purposes was 

 gunpowder. With the discovery of guncotton and nitroglycerine, 

 gunpowder was gradually replaced by them for blasting purposes. 

 In their early days the two explosives were used singly, guncotton as 

 guncotton, nitroglycerine — first of all alone, and then as dynamite. 

 Later on the two were combined as " blasting gelatine," and explo- 

 sives of a similar nature, but it was quite forty years after their dis- 

 covery before either became of practical use for propulsive purposes. 

 At the present time, smokeless powders made from the violent gun- 

 cotton, or of guncotton combined with the still more violent nitro- 

 glycerine, have almost entirely superseded the old-time gunpowder. 

 Modern explosives are characterized by very greatly increased power, 

 giving enormously greater range to projectiles fired from both rifles 

 and artillery, thus altering entirely the condition of both land and 

 naval warfare. 



Besides the hexa-nitrate of cellulose, or guncotton, lower ni- 

 trates may be formed by using more dilute acids, and altering the 

 conditions somewhat. These lower nitrates differ from the hexa- 

 nitrate in being less explosive, although highly combustible, and are 

 soluble in various liquids, including alcohol and ether, in which gun- 

 cotton is insoluble. When these lower nitrates are dissolved in a 

 mixture of ether and alcohol we have the useful substance " collo- 

 dion," which, when applied to a wound, leaves, upon evaporation of 

 the ether and alcohol, a film of these lower nitrates, usually called 

 " collodion wool " or " cotton." " Celloidin " wool is the purest 

 form of collodion wool and is neither inflammable nor explosive. It 

 burns, however, if brought into contact with a naked flame. It is 

 used for photographic purposes almost exclusively. 



Celluloid is an intimate mechanical mixture of pyroxyline (gun- 

 cotton or collodion cotton) with camphor, formed by adding the 

 pyroxyline to melted camphor, or by strongly compressing the two 

 substances together, or by dissolving the constituents in an appro- 

 priate solvent, e.g., alcohol or ether, and evaporating to dryness. A 

 combination of the two latter methods, i.e., partial solution, with 

 pressure, is now usually adopted. The pyroxyline employed is 

 generally the tetra- and penta-nitrated cellulose, the hexa-nitrate 

 (guncotton) being but seldom used on account of its explosive pro- 



