488 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



paraffin will effectually preserve it from deterioration by the 

 action of the weather. The j^araffin, it is said, hardens the 

 plaster so much that the finger-nail will scarcely scratch 

 it, increases its weight considerably, gives it an ajjpearance 

 of transparency like ivory, and preserves it though subjected 

 to repeated washings. The process of saturation is stated 

 to be similar to that employed in the saturation of plaster 

 casts in stearin. 



IMPROVEMENT IN PLASTER OF PARIS. 



A new process of manufacturing plaster of Paris is an- 

 nounced, which is said to afford excellent casts, that set slow- 

 ly, and are of a pure white color. The process consists briefly 

 in immersing the unburnt gyjisum for fifteen minutes in wa- 

 ter containing ten per cent, of sulphuric acid, after which it 

 is calcined. 



'WATER-PROOF DRESSING FOR LEATHER. 



A dressing for rendering leather water-proof, made as fol- 

 lows, as proposed by Hager, has been found to answer the 

 purpose : Soften one part of India rubber in five j^arts of 

 illuminating petroleum, by digestion for a day, and add 

 twenty parts of paraflin to the pasty mass, and digest again 

 for half a day, with repeated stirring, and then mix it with 

 five parts of oil and five of tallow, and finally add ten of 

 petroleum, or enough to give the mass the consistency of 

 butter. 8 C, February 11^ 18'75,55. 



EFFECT OF FREEZING UPON THE COLOR OF FABRICS. 



The reduction of the color of indigo blue on cotton by 

 freezing, noticed by Kochlin, is ascribed by Goppelsroder to 

 ozone in the air, which, he found by experiments, acts at 

 temperatures below the freezing-point, if the material is not 

 dry. He found that cochineal red on wool was decidedly 

 weakened, but not bleached, after a week's exposure to 

 ozone ; aniline black remained unchanged ; aniline brown on 

 cotton became yellowish-orange ; fuchsin, aniline blue and 

 violet, corallin, and iodine green were bleached, as well as 

 dyewood lakes, and even Turkey red. Ozone is also very 

 effective in developing certain colors. This action is very 

 decided in the case of aniline black, which is developed by 



