M. TECHNOLOGY. 501 



to run freely from the point and to give a fine stroke. A so- 

 lution of gum arabic may also be kept fluid by the addition 

 of half its bulk of glycerine. 18 C, March 6, 1872, 155. 



PRINTING ON GLASS. 



Type made of an elastic material is used, and printing-ink, 

 with which is mixed fluoride of calcium. The glass thus 

 printed on is then heated to a suitable temperature with sul- 

 phuric acid, and, after having been washed with water, it ex- 

 hibits in indelible engraving the figures of the type. 16^4, 

 January, 1872, 110. 



USES OF CUPRO-AMMONIUM. 



It was announced, not long ago, that when copper scraps 

 are immersed in concentrated liquid ammonia, a deep blue 

 fluid is produced, called, provisionally, cupro-ammonium, pos- 

 sessing a remarkable solvent power for paper, linen, silk, and 

 bone, and various practical suggestions have been made for 

 its utilization. We now learn that among the articles exhib- 

 ited at the London International Exposition of 1872 is a mod- 

 el of a house, built entirely of paper, rendered water-proof by 

 this process, a simple immersion being sufficient to accom- 

 plish the object. To show the water-proof character of this 

 paper, a stream of water is made to flow over the model con- 

 tinually. Two sheets of paper, moistened with this substance 

 and pressed together, become indissolubly united ; and this 

 application has already been utilized for making paper bags, 

 where no danger is likely to arise from the poisonous nature 

 of the copper. 16 A, July, 1872, 412. 



GELATINE MOULDING. 



The introduction of a process of casting known as gelatine 

 moulding, which has come into vogue within a few years, has 

 proved to be of great value in taking casts of delicate and 

 intricate objects without showing any seam. For this pur- 

 pose, the object to be copied, whether in plaster or of other 

 material, is properly coated with oil and soap, to prevent ad- 

 hesion, and then covered with canvas for protection. Rolls 

 of modeling clay are then laid on over the canvas, until the 

 whole surface is covered to a suitable thickness, say from 

 four to six inches, and against this a plaster coating or wall 



