Proceedings of Learned Societies. 303 



the cotton yarn is dried in a centrifugal drying machine, and im- 

 mersed in a mixture of one part of nitric acid (specific gravity 

 1*5),™ and three parts of sulphuric acid. Contrary to the original 

 directions of Schonbein, it is allowed to remain immersed for forty- 

 eight hours, so as to secure uniformity of result. During this 

 action great care is taken to prevent the temperature rising. The 

 cotton is then washed in a stream of water for a period of time vary- 

 ing from one to three weeks, and is subsequently dried in the open 

 air ; during this stage of the manufacture, some experiments have 

 been tried as to the effect of steeping it in a solution of soluble 

 silica prepared by dialysis, apparently with satisfactory results. 



The properties of gun-cotton as prepared by the Austrian process 

 appear to be very uniform and certain. When loosely arranged it 

 inflames at a temperature of about 300° Fahrenheit, burning without 

 smoke, and without leaving any ash. Its rapidity of ignition is so 

 great that it does not ignite gunpowder when laid on its surface 

 and exploded. By pressing a thin edge, as that of a stout card, on 

 the centre of a tuft, one portion may be ignited without the flame 

 communicating to the other. When gun-cotton is twisted into a 

 yarn, its rapidity of combustion is perceptibly diminished ; by vary- 

 ing the degree and tightness of the twist, the exact rate of burn- 

 ing required for different purposes can be secured, from the explosive 

 violence necessary to propel balls from cannon to the slow combustion 

 desirable in a mining fuse. An explosive gun-cotton resolves itself 

 into gases, which are themselves combustible in air, consequently 

 when a flask of gun-cotton is burnt in an open glass vessel, a secon- 

 dary flame is seen, caused by their combustion. 



Although the combustion of gun-cotton does not depend on 

 atmospheric oxygen, its mode of burning is remarkably affected by 

 the character of the gases in which it is burnt ; thus in carbonic 

 acid it burns with a feeble flame ; iu hydrogen, with one still 

 feebler ; in a receiver exhausted to a vacuum of 3 inches, it burns 

 with a very slow combustion without light. The conditions 

 requisite to the rapid burning of gun-cotton are, that the gases 

 produced by the combustion should communicate sufficient heat to 

 the adjacent portions to carry on the combustion. Hence, in gases 

 like hydrogen and coal-gas, whose conducting power is very great, 

 the heat produced is carried away so rapidly that the cotton almost 

 refuses to burn. 



By heating a twisted yarn of gun-cotton gently, a very slow 

 combustion may be produced, or the same effect may be caused by 

 blowing a current of air on a yarn in rapid combustion. The ease 

 with which different rates of these combustions may be alternated 

 was very strikingly demonstrated by Prof. Abel, who, after produc- 

 ing the slow rate of burning in a horizontal yarn, caused the com- 

 bustion to become instantaneous by raising it to the perpendicular 

 position, with the inflamed part dependent. Also, after having 

 produced rapid combustion in one end of a long yarn, he changed 

 it into the slow combustion by blowing the flame away from the 

 unconsumed cotton, and back again to the rapid burning by blowing 

 the current in the opposite direction. 



