160 ANNUAL OF SCIENTIFIC DISCOVERY. 



upon the iodide of sulphur with which it is coated, and it receives the 

 photographic image within a minute. The glass plate, when taken 

 out of the camera, only exhibits a trace of the picture, but this 

 immediately comes out on exposure to the action of the vapor of bro- 

 mine. If the picture be now held over alcohol, and some of the same 

 liquid be poured upon it, it will be fixed. 



The glass plates must be breathed upon and well rubbed with a soft 

 linen rag several times before use. They are coated with sulphur by 

 burning sulphur sticks, made on purpose, in a proper tube, and hold- 

 ing the plates over it at a distance of about three inches. These 

 sulphur sticks are prepared by dipping pieces of rush pith into a 

 melted mixture of sulphur and mastic, with which they become 

 incrusted. For use, these sulphur sticks, which are about the size 

 of a lucifer match, are stuck on a brass needle, introduced into the 

 middle of a glass tube, and kindled, so that the vapor of the sulphur 

 may come in contact with the glass plate held over it. 



These glass plates are so sensitive, that the coating of iodide of 

 sulphur becomes instantly changed on exposure to direct sunlight, 

 and give a Moser's image within five minutes when laid in a book. 

 The figures thus obtained are most easily read by candlelight. In 

 daylight, the blue letters can be recognized on the yellow ground 

 only by looking through the plate towards the middle of the window, 

 or towards a sheet of paper fastened in that place, the sulphur not 

 having been removed either by vapor of bromine, or by alcohol. 



If a glass plate, covered with a solution of gum and exposed to the 

 vapor of iodized sulphur, be placed in the camera, a positive picture, 

 with all its details, is obtained, the outlines of which can be laid bare 

 by an etching point capable of scratching the glass. If a glass plate, 

 so marked, be rubbed in with printing ink, the outlines will be filled, 

 and the ink will remain in them when the glass is freed from the 

 coating of gum by means of water. The picture is then easily trans- 

 ferred to paper, which is to be laid on the plate and rubbed over with 

 a paper-knife. 



Improvements in preparing photographic paper. M. Legray, in a 

 recent communication to the French Academy, describes a new 

 method of preparing photographic paper, which he claims to possess 

 superior qualities. The substance first used in the preparation of the 

 paper, is virgin wax, which is kept at a temperature of 100 Centi- 

 grade, in a large, flat vessel, and the paper is immersed therein until 

 completely saturated with the wax. The sheet of paper is then 

 withdrawn, and laid between several pieces of blotting paper, over 

 which a moderately heated iron is passed, which causes the blotting 

 paper to absorb the superfluous wax. If the paper is properly pre- 

 pared, there will be no gloss whatever on its surface, and it will be 

 perfectly transparent. 



The waxed paper is then immersed in a warm solution, composed 

 as follows : 



