M. TECHNOLOGY. 519 



on cloth with this liquid, by means of a quill, are fixed, after 

 they have become dry, by pressing the cloth on the other 

 side with a hot iron. The ink will keep in well-closed bot- 

 tles for a long time without separation of the suspended cin- 

 nabar. 6 G, September 10, 1874, 368. 



SUBSTITUTE FOE INK. 



A substitute for ink has been devised by Dr. Jacobsen, 

 of Berlin, which consists of points, like the leads of ordinary 

 pencils, that can be fitted into holders. The writing at first 

 very much resembles lead-pencil marks, but when moistened 

 immediately assumes a violet tint, and then adheres to the 

 paper like ink. As many as six good copies can be taken 

 from it by means of an ordinary copying -press. 5 C, LI., 

 1874,449. 



THE HARDENING OF PLASTER OF PARIS. 



Landrin distinguished three phases in the hardening of 

 gypsum by watching its progress under the microscope : 

 (1) the assumption of a crystalline condition by the calcined 

 plaster in contact with water ; (2) the solution of a certain 

 portion of the crystal by the surrounding water; (3) the 

 evaporation of a certain amount of water by reason of the 

 heat generated in taking up the water of crystallization and 

 the formation of a crystal, which effects the crystallization 

 of the whole mass, just as a crystal in a supersaturated solu- 

 tion of a salt. During the first two phases no hardening 

 takes place, and it is only after some time that the maximum 

 degree of hardness is reached, and the amount of water then 

 present is only double that in the ordinary hydrate or gyp- 

 sum. A definite mixture of water and plaster, which hard- 

 ened in ten minutes, was found to lose water gradually for 

 eighteen days, until the above composition was reached, when 

 there was no further loss of water. 18 C, Oct. 14, 1874, 648. 



SETTING OF PLASTER OF PARIS, AND MIXTURE OF LIME 



WITH IT. 



According to Landrin, the setting of plaster of Paris is 

 retarded by any thing unfavorable to crystallization, as by 

 the use of a large quantity of water, in which case, however, 

 the mass becomes very porous ; or better still, by the addi- 



