M. TECHNOLOGY. 511 



twice the quantity of shellac to the naphtha, place the whole 

 in an iron vessel, apply heat cautiously, stir till well mixed, 

 and then pour out on a slab to cool. 18 A^ XXIL, 97. 



DURABLE GLUE. 



A very permanent and durable glue, which may be called 

 chrome glue, is made by adding to a moderately concentrated 

 solution of the glue one part of acid chromate of lime in solu- 

 tion to five parts of gelatin, this salt of chrome being thought 

 better adapted to the purpose than bichromate of potash, 

 which is usually used. The glue thus prepared, after being 

 exposed to the light, becomes insoluble in water, in conse- 

 quence of the partial reduction of the chromic acid. This 

 preparation can be used in cementing glass objects liable to 

 be exposed to boiling water, the treatment being the ordi- 

 nary one of applying the glue to both surfaces of the frac- 

 tured object, and then binding them together until dry, and 

 exposing them for a sufficient length of time to the light, 

 after which boiling water will have no action upon them. 

 It is suggested that this preparation will be better adapted 

 to cementing the covers on glass slides than any now in use. 

 The same preparation can be applied for making fabrics wa- 

 ter-proof, especially sails of ships, awnings, etc., where no 

 great flexibility is necessary. Two or three applications of 

 the glue, either by inmiersion of the object in it or by the 

 use of a brush, will answer the purpose. Roofing-paper is 

 also rendered impervious, even when exposed to long-con- 

 tinued rains. 13 B^Fehruary 6, 1876, 158. 



WATER-PEG OF AWNINGS. 



Awnings can be rendered water-proof by plunging the 

 fabrics into a solution containing twenty per cent, of soap, 

 and afterward into another solution containing the same per- 

 centage of sulphate of copper. Wash, and the operation is 

 ^\\\^\iQdi. Engineer, No. 1034, 281. 



LIQUID GLUE. 



Dilute officinal phosphoric acid with two parts by weight 

 of water, and saturate with carbonate of ammonia; dilute 

 the resulting liquid, which must still be somewhat acid, with 

 another part of distilled water, warm it on a water-bath, and 



