PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION, 59t 



be more readily obtained. But gun cotton has another value, 

 for it is the foundation of the art of photography as it now 

 etands. It has been suggested that cotton should be dissolved 

 in hydrocholoric acid, that any desired form should then be given 

 to it and the acid evaporated. This can be done, but the cotton 

 thus precipitated has no strength. Its strength is caused by its 

 fibers. The composition of cotton, sugar, starch, gum arabic, 

 dextrine and woody fiber is chemically the same, C H . 



12 10 



Gun cotton is chemically different. Two or three atoms of hydro- 

 gen are taken away and two or three atoms of the peroxyd of 

 nitrogen, NO , are substituted. Yet this change does not aflFect 



the appearance of the cotton, even when examined by the most 

 powerful microscope. But upon trying it with the polariscope, 

 we find that the effect upon polarized light is precisely the re- 

 verse of that produced by the ordinary cotton. Dr. Van der 

 Weyde states that he has converted cotton into sugar. The cot- 

 ton is boiled in an acid for some time. First it is changed into 

 dextrine, and then into sugar ; but it is grape sugar, and will 

 not crystallize. The composition of sugar is nearly the same as 

 that of cotton and woody fiber ; it is C H . 



12 12 12 



Mr. Pell stated that in Lowell, within the last year, a pound 

 of cotton had been spun into a thread 358 miles long. 



Mr. Seely had seen a statement that, in England, 1,096 miles 

 had been reached ; but that seemed hardly credible. ^ 



Mr. Babcoclc. — Cotton is also valuable because it is soft and 

 elastic, and hence it is used in cushions and for similar purposes. 

 It is also used in a form in which it is harder than iron itself, for 

 the rollers of calendaring machines. Compressing cotton by 

 hydraulic pressure, a roller is produced so hard that it can be 

 turned like iron in the lathe, and forms a polished, smooth sur- 

 face, so hard and elastic that, even with a sledge hammer, no 

 permanent indentation can be made. The rollers are manufac- 

 tured in Providence, R. I. 



Mr, Garbanati. — Wool could nof be profitably grown for cloth- 

 ing alone, and the demand for the meat being limited, wool must 

 be limited in its production. Silk is expensive, and must be con- 

 fined to special uses. Flax is objectionable because it is too 

 good a conductor of heat to be worn next to the skin. Hence it 

 is important to find some substitute for cotton, so that we maj 



