598 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Prof. Abel said some experiments made bj^ him some years ago, upon 

 the preservation of canvas, led him to believe that oxidisation was not 

 the cause, but he would rather attribute it to a mechanical force of crystal- 

 ization. The experiments he referred to were made under conditions very 

 similar to those described by Dr. Calvert. The canvas or tent duck was 

 ■first impregnated with a solution of basic acetate of lead, and subsequently 

 immersed in aqueous silicate of soda, which had the effect of precipitating 

 a dense silicate of lead within the fibre. The canvas thus prepared was 

 found to be very considerably protected against fire and the attack of mil- 

 dew ; but there was a diminution in the strength of the material, and the 

 process had to be abandoned. As a confirmation of the correctness of his 

 opinion, Mr. Abel mentioned the result of other experiments in which flax 

 and cotton fabrics were impregnated with the sulphate of magnesia, a 

 neutral salt which could not exert or promote chemical action upon the 

 fibre, yet the material became weakened merely in consequence of the depo- 

 sition of solid matter within the fibre, and the unusual distension of the 

 latter by the act of crystalization. 



Manufacture of Indiarubber Combs 



Dr. Parmelee being called upon to open the regular subject of the even- 

 ing, the manufacture of combs, remarked that he had designed to speak 

 onl}^ of combs made from hard rubber. Exhibiting a black mass, he said 

 that it was a specimen of the rubber after being masticated — that is, passed 

 between hot rollers, one of which revolves a little more rapidly than the 

 other, and thus grinds and kneads the substance into a homogeneous mass. 

 He then exhibited a specimen of the rubber after being mixed with the sul- 

 phur. It was a light colored, limber, elastic sheet. The speaker remarked 

 that hard rubber differs from soft vulcanized rubber only in containing a 

 larger proportion of sulphur, and being subjected to a higher temperature 

 and for a longer period. It was invented by a younger brother of Mr. 

 Charles Goodyear, the author of the great discovery of vulcanized rubber. 

 The materials are mixed in various proportions, ranging from four to six- 

 teen ounces of sulphur to the pound ot rubber. The best proportion is 

 that of equal parts of sulphur and rubber. After the two ingredients are 

 thoroughly incorporated, the sheets are rolled down to about one-sixteenth 

 of an inch in thickness, and are then subject to a temperature of 280° for 

 eight hours. In order to keep the surfaces of the sheets smooth, they are 

 oiled on both sides with a solution of lard in petroleum, and covered with 

 a very thin sheet of block tin. They are then placed either in a pan of 

 water or in a tight soapstone box, and enclosed in a strong air-tight cylin- 

 der, where they are heated to the required temperature. 



The speaker stated that hard rubber may be softened by immersing it in 

 boiling water, or otherwise raising its temperature to 212°. It can then be 

 stamped, pressed, or molded into any desired form. Combs are made by 

 pressing the substance into the proper form, while it is thus softened, and 

 then cutting the teeth. There are three processes for cutting the teeth. 

 By one process each 'tooth is cut separately by a circular saw. A small 

 machine has been invented by which the comb is fed to the saw, drawn 

 back automatically and carried forward to the next tooth till the comb is 



