Progress of Invention. 4H1 



in a solution of gum tragacanth and gluten, then dried and rolled ; 

 after which it is coated with a solution of caoutchouc in benzole. 

 It is next spread out on glass, and, having been inclosed in a 

 frame, is left to dry. It is then sensitized with perchloride of 

 iron and tartaric acid, and a picture is printed on it in the usual 

 way. The development is effected by a mixture consisting of two 

 parts double salt of gold and three parts gold in powder; a current 

 of hydrogen is next thrown upon it to reduce the metallic salt, 

 after which the silk is separated from the glass. The side of the 

 silk containing the picture is now pressed against a plate of clean 

 copper, which has been previously coated with a mixture consisting 

 of concentrated chloride of zinc, borax, carbonate of ammonia, and 

 gum, and has been allowed to dry until the coating becomes sticky ; 

 it is then rubbed with a damp sponge, after which the silk is- 

 drawn away. The picture remains on the plate ; and the flame 

 of a soldering lamp having been thrown upon it, it is exposed in 

 a camera. The design, damascened in gold, is thus obtained on 

 the copper plate ; and when the latter is ac^ed upon with a solution 

 containing ten per cent, nitrate of silver — which does not eat under 

 the protected portions — a film of copper is removed from the un- 

 covered portions. The silver thus reduced is taken away by wash- 

 ing, and the plate is again exposed to the action of the nitrate ; 

 the same thing being repeated a number of times in succession, 

 until sufficiently deep hollows have been formed. 



Application of Heat in Mining. — The use of heat, in the 

 crumbling down and removal of rocks, is of very ancient date ; it 

 has been latterly applied in the mines of the Hartz mountains, very 

 advantageously, to the separation of considerable masses of ore. 

 Tor this purpose, a small furnace is placed against the face of the 

 rock containing the mineral, and the coke with which it has been 

 supplied is kept in a state of ignition for some hours ; after which 

 the furnace is withdrawn, and the heated portion of the rock is 

 sprinkled with water. In a short time a large mass separates, and 

 an additional quantity not long after. On the whole, a mass several 

 inches in depth, and of considerable weight, is thus removed, and 

 at a cost fifty per cent, less than if gunpowder had been employed. 



Erasine.— Grease, etc., is readily dissolved by benzine ; but 

 the latter has the disadvantage of an offensive odour. A new 

 substance has, however, lately been discovered which possesses the 

 useful properties of benzine, while, at the same time, any odour it 

 emits is agreeable. It has been called Erasine, and is the product 

 of a species of pine, accidentally discovered by some persons who 

 were collecting turpentine, and remarked that none could be 

 obtained in the usual way from certain trees ; but instead of it, a 

 juice possessing the power of dissolving all animal and vegetable 

 oils, without leaving any stains, or injuring the most delicate colours. 

 Erasine has already found its way into commerce, and it would 

 answer well for burning in lamps, but that it is too dqar. 



Newly-observed Source of Magnetism. — A source of magnet- 

 ism has been discovered which, it is probable, has not been remarked 

 before ; and it is the more deserving of attention since it seems to 



