812 SUMMARY OF CURRENT RESEARCHES RELATING TO 



2)orcentago composition is GO parts (by weiglit) chlorate of potash, 

 30 parts luagnosium in powder, 10 parts sul^jhide of antimony. The 

 combustion of this powder is effected in a lantern L, the body of which 

 is a metal tube, closed at one end and provided at the other with a glass 

 plate aud a diapliragm, the aperture of which corresponds accurately with 

 the diameter of the illuminating lens. Within the lantern, aud on a 

 level with its central point, is a metal i)late, upon which the powder and 

 touch-paper are placed. On the left side of the lantern is a slit closed 

 by a shutter ; through the slit the touch-paper is lighted. Tlie lantern 

 is further provided with a chimney, bent at an angle and about 5 metres 

 long. The chimney, which tits on the lantern, is not shown in the 

 illustration. About 0*75-1 metre from its end the chimney is fitted 

 with a special ajiparatus for absorbing the smoke. 



The camera is placed vertically and the illuminating lens B horizon- 

 tally. The preliminary focusing is made with a mineral-oil lamp, after- 

 wards exchanged for the lantern. 



For instantaneous photography the sensitiveness of the plate must 

 be known, and to estimate it for tliis maguesium powder the author has 

 devised a special sensitometer. This consists of a glass plate 12 x 15 

 cm., divided np into thirty rectangular spaces of 2 x 3 cm. and covered 

 with tissue paper. The spaces are numbered according to the number 

 of layers of jiaper. This sensitometer is fixed in a copying frame and 

 then inside a pasteboard box open in front. The frame is then placed in 

 a room lighted by a candle and exposed for a certain time. The ordinary 

 develojier is used, but without the addition of bromide. Then the 

 number on the sensitometer gives the sensitiveness of the plate. The 

 author's results were obtained from stearine caudles (eight to the pound), 

 distance 30 cm., exposure one minute, and developing five minutes with 

 the pyrogallic developer ; he found that plates 22 and 23 were quite 

 distinct, and that No. 21 was almost as good. 



As most objectives differ more or less in their focus, it is obviously 

 advisable to obtain a filter which will permit sharp photographic 

 pictures to be produced by their aid. A mixture of copj^er nitrate and 

 chromic acid in water allows only 7 per cent, of all spectrum colours to 

 pass through (or diluted 12-14 per cent.). By using this as a light 

 filter in combination with ei-ythrosin the focal differences are quite ob- 

 viated. As dry plates are not usually obtainable in a condition suitable 

 for the erythrosin emulsion, wet plates are recommended. All opera- 

 tions with these plates must be conducted in a very subdued red light. 

 Mixtures of erythrosin aud silver nitrate give precipitates of a silver 

 compound which are very sensitive to yellow light, and act more power- 

 fully in bromide-gelatin than the pure dye. For making this mixture 

 the following formula is given : — 25 ccm. erythrosin solution, 1 : 1000 ; 

 1 ccm. silver nitrate solution, 1 : 80 ; 1/2 ccm. ammonia ; 75 ccm. water. 

 The plates are bathed therein for one minute and dried in the dark. 



Photographing moving Microscopic Objects.* — M. L. Errera pro- 

 poses to apply to microscopic objects the process already employed for 

 recording each phase of the movement of a horse, &c., more especially 

 the plan adopted by Anschlitz in his " Schnellseher," which is fixed in 

 a dark chamber which that author describes as follows : j — " The succes- 



• Bull. Soo. Belt;. Micr., xiv. (1887) pp. .S2-5. 

 t Catalogue of the "Wiesbaden Exhibition, 1SS7. 



