M. TECHNOLOGY. \ 611 



alum melts, and the 52 per cent, of water it contains escapes 

 into the powder-chest, through small openings, and prevents 

 the explosion of the powder. The safes were placed in sep- 

 arate furnaces, and after being heated intensely for six hours, 

 the powder in two of them, on examination, was found unaf- 

 fected, the chests themselves appearing in good condition, 

 and a re2:isterino; thermometer indicatinsj a maximum of 210. 

 The two remaining chests were heated still further without 

 damage. 14 C, 1873, CCVIIL, 234. j 



IMPEOVEMENT IN PHOTOLITHOGRAPHY. ; 



In the ordinary process, paper coated with a mixture of 

 bichromate of potash and gelatine, and exposed under a suit- 

 able negative, is covered with fatty ink, and immersed in hot 

 water, which dissolves the unchanged gelatine, and leaves 

 the picture coated with fatty ink, wiiich is then transferred 

 to a suitably prepared stone. By this method fine lines are 

 not faithfully reproduced, since the hot water swells the 

 insoluble gelatine, and softens the fatty ink. Paul avoids 

 this defect by dispensing with heat in removing the un- 

 changed portion, substituting albumen for gelatine. The 

 roughening, of even the finest quality of paper, on being 

 moistened, is prevented by employing the ivory -surfaced 

 transferring paper of the Autotype Company, prepared with 

 a mixture of equal parts of beaten albumen and a saturated 

 solution of bichromate of potash. After proper exposure 

 under a negative, it is placed on a lithographic stone, which 

 has been covered with ink, and passed through the press sev-^ 

 eral times, changing its position each time. On soaking it 

 in a vessel of cold water for some time, the unchanged albu- 

 men dissolves, and can be removed by brushing lightly with 

 a sponge, afibrding a very fine, sharp picture, ready for trans- 

 fer to the stone by simple pressure, the cold water having 

 no injurious effect upon the picture or the ink, while the 

 paper retains its fineness of texture. 15 (7, XII., 1873, 189. .; 



MACHINE FOR REPRODUCING ALL KINDS OF ART-MODELS. 



A machine, that may prove of value to founders, etc., has 

 been devised by G. Mathis, of Villingen, which is said to be 

 capable of producing a perfect copy of a piece of sculpture 

 of any size or shape, with great rapidity and precision, and 



