534 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



to draw off and strengthen the bath. As the deeper shades 

 are successively imparted in diminished quantities of bath, 

 which alone need be of the required strength, the economy 

 of the process is apparent. It is said to be secretly employed 

 in some establishments. 24 (7, 1874, 137. 



WEATHER-PROOF COATING FOR ZINC. 



According to Puscher, the addition of sesquioxide of iron 

 to a solution of basic acetate of lead affords a fine brownish- 

 red permanent coating for zinc ; and by the substitution of 

 other pigments lighter or darker coatings, of any desired 

 shade, may be imparted to architectural zinc castings. Deep 

 black, permanent characters may be formed on clean sheet 

 zinc by writing upon it, with a steel pen, with a solution of 

 equal parts of chlorate of potash and sulphate of copper, in 

 thirty-six times the quantity of hot water, and washing and 

 drying the zinc after a few minutes. This fact may be es- 

 pecially useful to gardeners. 15 (7, 1874, xi., 174. 



WATER-PROOF COMPOSITION FOR COATING FABRICS. 



Material coated, by means of a brush, with the following 

 composition (patented in England), and then dried and ex- 

 posed to the light, is said to become water-proof: Oil, var- 

 nish, and glycerine are added to a solution of caseine in am- 

 moniacal water, and the mixture is boiled, and bichromate 

 of potash added to it after cooling. 6 C, May 14, 1874, 198. 



PREPARATION OF STARCH PASTE. 



It is best to prepare paste by triturating the starch with 

 cold water in a mortar until no lumps remain, and not too 

 thick a mass is formed, and pouring into this boiling water, 

 very slowly, with rapid stirring, until the paste begins to 

 form, as indicated by the increase of transparency, and then 

 rapidly adding the rest of the boiling water necessary for 

 the paste. Boiling the paste is very injurious, rendering it 

 less adhesive, and liable to peel off. Rye flour affords "a more 

 adhesive paste than starch, but of a gray color. The addi- 

 tion of a little alum to the water with which paste is pre- 

 pared renders it more permanent, and the use of boiling lime- 

 water instead of pure water adds to its adhesiveness. An 

 aqueous extract of decomposed gluten, however, affords the 



