M. TECHNOLOGY. 489 



paper by lamp-light, and after washing the latter with water 

 a negative of the drawing remains, since the portions of the 

 coating acted on by the light become insoluble in water. 

 From such a negative any number of positives can be taken 

 in the same way. 14 C\ 1874,CCXI.,49. 



PREPARATION OF PHOTOGRAPHIC TRACING-PAPER. 



A paper sensitive to light, brought into the market by Tal- 

 bot, of Berlin, under the name of " Lichtpauspapier," by 

 means of which any one unskilled in photography may copy 

 plans, maps, etc., with little trouble, may be perfectly imi- 

 tated by floating good strong albumenized or arrow-root pa- 

 per, for about a minute, on a bath composed of water, thirty- 

 two parts ; nitrate of silver, three parts ; citric acid, one part ; 

 and tartaric acid, half a part; then drying it, and finally draw- 

 ing it slowly through a weak solution of tartaric acid. It 

 will keep at least three months, if protected from light and 

 moisture, and does not require fuming with ammonia. Ton- 

 ing, which is in most cases superfluous, requires a very strong 

 alkaline bath. 5 (7, 1874, xn., 96. 



A VERY SIMPLE PANTOGRAPH. 



Schnaus suggests the use of a fine rubber cord, about fifteen 

 inches long, supplied with a loop at each end, and having on 

 it a small white bead, sliding upon it with gentle friction. By 

 securing one end to the table by a pin, and passing a pencil 

 through the other end, and drawing its point over the paper 

 with the right hand, keeping the string stretched, and caus- 

 ing the bead to describe the outline of a simple drawing- 

 placed beneath it, a tolerably good copy of the drawing will 

 be produced, bearing any desired proportion to the original, 

 according to the position given to the bead on the string; 

 thus, if the bead is in the centre of the cord, the drawing will 

 be double the size of the original. The best results are only 

 obtainable after some practice, and by employing a finer point 

 than a bead. 5 (7, 1874, iv., 31. 



WATER-PROOF TISSUE-PAPER. 



A paper unaffected by water or oily matter, possessing the 

 external appearance of parchment-paper, and suitable for 

 tracing-paper, may be produced, according to R. Jacobsen, 



X 2 



