Septembeb 3, 1909] 



SCIENCE 



315 



be reduced by boiling with a spiral of heavy alu- 

 minum wire and titration with permanganate 

 after the removal of the aluminum wire spiral and 

 addition of excess of ferric sulphate. 



In the analysis of carnotite ore after solution 

 of the ore in nitric acid and evaporation with 

 sulphuric acid the vanadium and uranium are 

 separated from iron by double precipitation of the 

 latter with sodium carbonate in the presence of a 

 little hydrogen peroxide. In the acidified solution 

 the vanadium is first determined by reduction 

 with sulphur dioxide to VjO, and titration with 

 standard permanganate, after which the vanadixim 

 is reduced by boiling with aluminum to V.O, and 

 the uranium to UO;. After complete reduction of 

 the uranium and vanadium acidified ferric sul- 

 phate is added and the solution titrated with 

 standard permanganate. 



The Development of Positives after Short Ex- 

 posures: Wiu)EB D. Banceoft. 

 If we expose a plate for ten minutes on a sunny 

 day, the plate will develop as a positive instead 

 of a negative. The theory of this phenomenon is 

 quite simple and I need not go into it now. My 

 problem to-day is how to produce the same result 

 with a short exposure in the camera as with a 

 long one, and we have worked out three methods 

 of doing this. 



The first way is to make the plate much more 

 sensitive to light. This can be done by dipping 

 the plate in a developer solution and exposing it 

 wet. The light acts in the presence of a powerful 

 depolarizer, the developer, and in consequence the 

 chemical action is much greater for a given ex- 

 posure. Incidentally, this method can also be 

 used for shortening the exposure necessary to 

 produce a negative. 



The second way is to expose the plate after it 

 has been in the camera to a uniform light for a 

 short time. Since the sensitiveness of the plate 

 to light of a given wave-length changes during 

 the exposure, we can change the amount of con- 

 trast by changing the color of the fogging light. 

 A more satisfactory result is obtained with a 

 greenish-blue light rather than by the white light 

 which has ordinarily been used. Since the in- 

 tensity of the fogging light is greater at the air 

 side of the film than at the glass side, the decom- 

 position of the silver bromide is consequently 

 greater there. By use of a suitable developer, we 

 have succeeded in developing a plate so that there 

 is a positive image on the air side and a negative 

 image on the glass side. 



The third method is that of a slow reduction 

 before development. If the films in a kodak are 

 not developed until several months after the ex- 

 posure, there is always the possibility of their 

 developing as positives. This is undoubtedly due 

 to slow decomposition of the film which reduces 

 the silver bromide to a lower stage and therefore 

 duplicates the effect of a longer exposure. We 

 have produced the same eflect in the laboratory 

 under somewhat definite conditions. The plate is 

 left for a long time in a very weak developer and 

 is then treated with an ordinary developer. As 

 was predicted, the plate develops as a positive 

 under these circumstances. 



A fourth method is to add sulpho-urea to the 

 developer as suggested by Waterhouse; This 

 method gives beautiful positives; but we are not 

 yet certain as to the theory and we are still work- 

 ing at this. 

 The Cotidensation of 'Water by a Substance in 



Solution: F. K. Cameron and W. O. Robinson. 



The condensation of water due to the presence 

 of dissolved electrolytes is calculated from accu- 

 rate specific gravity determinations on solutions 

 of concentrations below 0.1 normal. In the cases 

 of solutions of hydrochloric and nitric acids the 

 concentration-condensation curves pass through 

 maximum points. The investigation was under- 

 taken primarily to find the effect of condensation, 

 by a substance in solution, on suspensions and 

 flocculation, but no generalizations of a causal 

 character can be made from the data obtained. 

 The Dielectric Constants of some Inorganic SoU 



vents: OscAB C. Schaefek and Hebman 



SCHLTJNDT. 



This communication is a continuation of the 

 earlier work of Schlundt on the dielectric con- 

 stants of inorganic solvents. The values obtained 

 for the three halogen hydrides — hydrogen iodide, 

 hydrogen bromide, hydrogen chloride — have been 

 determined. The value of the dielectric constant 

 of solid hydrogen cyanide is also reported as new 

 va'ue, that of the liquid having been published 

 some years ago. 

 Solvents for Use vnth the Munroe Crucible: Otis 



D. Sweet. 



About forty-five solvents are enumerated. A 

 table including about 120 precipitates and the 

 corresponding solvents is also given. 

 Organic Amalgams: H. N. McCoT and W. C. 



MOOBE. 



Discoveries in radioactivity in the last decade 

 clearly show that some, at least, of the metallic 



