202 ANNUAL OF SCIENTIFIC DISCOVERT. 



EXTRACTION OF OXYGEN FROM THE AIR. 



]\DI. Lairc antl jNIontmagnon propose to take advantage of tho 

 •woll-knowu property of wood charcoal, alkaline solutions, and 

 Mood, of absorbing a larger portion of o.\ygen from the surround- 

 ing air than of nitrogen. It is proved, by experiment, that 100 

 measures of wood charcoal, freshly burned, absorb 985 of oxygen, 

 and only about 705 of nitrogen. Tiie blood of animals and solu- 

 tions of phosphate and carbonate of sodium absorb rai)idly, ac- 

 cording to the amount of surface exposed to the air, about 12 per 

 cent, of oxygen, and only two per cent, of nitrogen. The pro- 

 posed method of utilizing these facts in this : — Pump out the 

 oxygen and nitrogen from the substances used to aljsorb it by 

 means of an air-pump; pass the mixture through fresh absorbing 

 media; re-extract, and repeat the operations as often as required. 

 In this way an oxygen is obtained ver}'' free from nitrogen, and 

 at an extremely cheap rate. — British Journal of Pliotograplnj. 



ENAMELS. 



The fine enamels of trade are generally prepared by fusing, at 

 high temperatures, silica, oxide of tin, and oxide of lead, and 

 sin-eading the mixture over the surface of a sheet of copper, of 

 gold, or of platinum. 



Tiie objections to these enamels are, in the first place, their 

 high cost, and, secondly, the impossibility of giving them a per- 

 fectly fiat surface. 



Mr. E. Duchemin has advantageously replaced them by the 

 following economical and elHcient compound: Arsenic, 30 parts 

 by weight; saltpetre, 30; silica (fine sand), 90; litharge, 250. 

 Tliis is spread on plates of glass of the required shape and size, 

 care being taken, however, that the kind of glass employed be 

 not inferior in point of fusibility to the enamel. 



Enamelled glass prepared from the above substances ma}' be 

 drawn or written on as readily as if it were paper, and in less 

 time than one minute the writing may be rendered indelible by 

 simply heating the plate in a small open furnace or mulllc. 



First-class photographs, either negatives or positives, may be 

 taken on such enamels without collodion, by using bitumen, or 

 citrate of iron, orperchloride of iron and tartaric acid, or bichromate, 

 or an}' other salt. 



A good solution for this purpose is, water, 100 parts by weight; 

 gum, 4 parts; honey, one; part; pulverized Ijichromate of potas- 

 sium, 3 parts. Filter the liquid, spread it over the enamel, and 

 let it rest, after which : — 



1. Expose it to the camera. 



2. Develop the image by brushing over it the following pow- 

 der: Oxide of coljalt, 10 parts l)y weight; black oxide of iron, 90 

 parts; red lead, 100 parts; sand, 30 parts. 



