146 ANNUAL OF SCIENTIFIC DISCOVERY. 



pared surface is treated as in taking an ordinary photograph, 

 either by placing it in the camera, or exposing it for a few seconds 

 under a positive, to the rays of the sun, or the magnesium or 

 electric light. 



The only thing remaining to state is the preparation of these 

 phosphorescent substances. One of the cheapest is Canton's 

 phosphorus, and it is made by burning oyster-shells for half an 

 hour, powdering and mixing with an equal weight of sulphur, and 

 heating again for one hour in a covered crucible. The produced 

 substance must of course be preserved in the dark, and protected 

 from moisture in a well-closed bottle. Wach found that the lumi- 

 nosity is much increased by moistening the mixture of shells and 

 sulphur, before the second heating, with a solution of sulphide of 

 arsenic in liquid ammonia. The powder thus obtained emits so 

 strong a light of blue color that it does not require perfect dark- 

 ness to perceive its glow. 



Baldwin's phosphorus, mentioned above, is prepared by dis- 

 solving chalk in nitric acid, then heating and grinding it to pow- 

 der. The Bolognian i)hosphorus is made by simply heating a 

 mixture of powdered heavy spar with the white of eggs, gum- 

 water, or a solution of tragacanth. Fluor-spar is naturally such 

 a phosphorescent substance, some specimens, however, more than 

 others, and diamond appears to be the best ; but the expense of 

 the powder would hardly admit of its employment for the above- 

 mentioned purpose. Experiments have proved this property, in 

 some degree, to exist in a great number of substances not sus- 

 pected to possess such a singular quality ; for instance, many 

 natural compounds of lime, baryta, strontia, and magnesia; be- 

 sides corals, fossil bones, and teeth ; the shells of eggs, oriental 

 pearls, dry bleached linen, white paper, and even the stones 

 extracted from the human bladder. 



Grott has found that the same luminous rays — the blue and 

 violet — which produce the jDhotograpliic pictures also produce 

 this effect, and that the rays which have no photographic powers 

 — red and orange — not only do not produce it, but extinguish 

 the existing luminosity. However, this is not because it is easily 

 extinguished, as handling and even immersion in water will have 

 no effect upon it, neither plunging the body in different gases. 

 Groszer found that the luminosity was not even in the least im- 

 paired in a perfect vacuum. — Scientific American. - 



IMPORTANT PHOTOGRAPHIC IMPROVEMENT. 



Mr. Joseph Buchtel, of Portland, Oregon, has recently devised 

 what is said to be a very important improvement in printing 

 pictures from negatives. ' The invention is described in the 

 ** Oregonian " as follows : — 



" There has already been a complaint among photographists, 

 that no perfect arrangement was known, by which an accurate, 

 clear, and sharp impression could always be taken. The trouble 

 has always been that no contact pad has been invented which 



