precipitation of uranate of potash. The salt is insoluble in alcohol which throws it down from an aqueous solution. This ammonia-citrate is the only compound of uranium which I have observed to be sensitive to sunlight in the dry state. The yellow powder turns dark brown on exposure to the direct rays of the sun. The change is far more striking with the solution, which rapidly acquires a deep brown red color without depositing a precipitate. This red solution turns yellow on standing a few days in an open glass, but preserves its color much longer in stoppered bottles. Owing to the presence of citric acid (which prevents precipitation after exposure as before) it is very difficult to determine what compound of uranium exists in this solution. On evaporating to dryness on a water bath a brown powder is obtained resembling that formed by exposing the dry salt. Potash produces in the red solution a green precipitate which gradually turns yellow. This reaction leads me to believe that the red solution contains the suboxyd U,O, discovered in 1863 by a French chemist named Guyard. By the prolonged action of zinc on the sesquioxyd dissolved in hydrochloric acid, Guyard obtained a deep red solution which furnished a green precipitate with alkalies.*

2

Nitrate of uranium is not only very soluble in water, alcohol and ether, but also in glycerine. Even when deprived of its water of crystallization the nitrate dissolves in pure glycerine.

The syrupy liquid exhibits the same behavior with reagents as an aqueous solution. On exposure to the sunlight the yellow solution turns green and finally becomes reddish brown without depositing a precipitate; no evolution of gas was perceptible. The brown liquid yields a dark brown precipitate with ammonia and this precipitate washed and dissolved in acids forms green solutions. It is probably a mixture of protoxyd and suboxyds. An aqueous solution of the nitrate with a few drops of glycerine, acquires on exposure a green hue and contains only the protoxyd. The transformation of the glycerine is reserved for further investigation.

Solutions of the sulphate, oxychlorid and oxyfluorid of uranium mixed with glycerine, are reduced in a similar manner; the double oxyfluorid of uranium and sodium (or potassium) is reduced more rapidly than with formic or oxalic acids, forming the green precipitate in an acid solution and the violet hydrate in a neutral one.

I have printed a number of photographs with solutions of various salts to which a small quantity of glycerine was added; by comparing these prints with those obtained without glycerine I have come to the conclusion that the addition of glycerine

Bull. Soc. Chim. 1864, i, 94.

both shortens the necessary time of exposure and quickens development. One minute's exposure yields a clear print when the paper is sensitized with the oxyfluorid of uranium and sodium with glycerine, whereas five to ten minutes is the time necessary in other processes. I recommend the use of glycerine to such photographers as may experiment with uranium pie

tures.

The actinic reactions of uranium salts much resemble those of iron; like the latter the sensitive uranium compounds all contain oxygen and the physical and chemical changes are due to complete or partial deoxydation. We also notice the necessary cooperation of organic matter, the part which the latter plays being clearly that of a reducing agent. Under influence of the actinic rays, the uranium salts part with some of their oxygen, which goes over to the oxydizable organic material. An aqueous solution of nitrate of uranium exposed to light in a glass vessel remains unchanged; but as soon as organic matter whether in the form of alcohol, ether, glycerine, cellulose or an organic acid, is brought in contact with the uranic solution a reduction is effected and the organic matter is oxydized at the expense of the uranium. Accordingly, salts of uranium with organic acids are for the most part sensitive as such. In the printing processes, cellulose effects the reduction, which is, however, assisted by the addition of alcohol (recommended by Hagen) or glycerine.

Attempts to obtain reactions with other agents than the actinic rays of the sun, gave negative results. A series of 23 uranium salts exposed to the light of magnesium wire, exhibited no fluorescence, nor was a solution of the oxyfluorid with formic acid reduced by exposure to the magnesium light. An experiment made with the intention of effecting reduction at a high temperature under pressure, was also unsuccessful. A solution of the oxyfluorid acidified with formic acid was heated in a sealed tube at 100° C., and afterward at 120° C. for many hours, but without producing the least change.

Details of manipulation, strength of solutions, &c., such as may be found in any practical work on photography, have been purposely omitted, it being my object to consider the subject strictly from a chemical point of view.

Description of Photographs.

No. 1. (Jan. 25, 1868.)-Common filtering paper sensitized with a mixture of oxyfluorid of uranium and potassium and formic acid. Exposed ten days. Fixed by washing. Barely perceptible outline.

The remaining experiments were made with unsalted nonalbumenized papier de saxe. The prints were well washed before development. An unvarnished negative was used.

No. 2. (March 11, 1869.)-Sensitized 1st with formic acid, 2nd oxyfluorid of uranium and sodium. Exposed one hour. Fixed (?) by washing. A weak print, green when first obtained, turned yellow on exposure.

No. 3. Sensitized with oxyfluorid of uranium and sodium mixed with glycerine. Exposed one hour-a violet print, which turned lemon-yellow on exposure.

No. 4. Sensitized with 1st, oxalic acid; 2nd, oxyfluorid of uranium and potassium. Exposed 15 minutes. Developed with ferricyanid of potassium-fixed by washing. A red picture.

No. 6. Sensitized with citrate of uranium and ammonia. Exposed 10 minutes. Developed with ferricyanid of potassium. A clear red picture.

No. 7. Sensitized with 1st, oxalic acid; 2nd, oxyfluorid of uranium and sodium. Exposed. Developed first with perchlorid and then with nutgalls solution. A blue black negative.

No. 8. Sensitized with oxyfluorid of uranium and sodium mixed with formic acid. Exposed 1 minute. Developed with ferricyanid of potassium. A weak red print not very clear.

No. 9. Sensitized with oxyfluorid of uranium and sodium mixed with glycerine. Exposed one minute. Developed with ferricyanid of potassium-a clear well defined red print.

No. 12. Sensitized with nitrate of uranium mixed with glycerine. Exposed 2 minutes. Developed with ferricyanid of potassium. An inferior red print.

No. 13. Sensitized with nitrate of uranium mixed with glycerine. Exposed 2 minutes. Developed with nitrate of silver and fixed with hyposulphite of soda. A fair print.

No. 14. Sensitized with oxyfluorid of uranium and sodium mixed with glycerine. Exposed one minute. Developed with nitrate of silver and fixed with hyposulphite of soda. An excellent well defined picture.

No. 15. Sensitizer S= oxyfluorid of uranium and sodium with glycerine. Exposed one minute. Developed with ferricyanid of potassium and then with perchlorid of iron. A brown picture which turned light blue while drying in the air.

No. 16. Sensitizer S. Exposed 1 minute. Developed with ferricyanid of potassium and then with protosulphate of iron. A well defined green picture.

No. 18. Sensitizer S. Exposed 70 seconds. Developed with 1st, ferricyanid of potassium; 2nd, mixture of same with perchlorid of iron. A clear snuff-colored print.

Employed following developing solutions.

A

B

C

=

=

1 grm. K,Fe, Cy, in 60 grms. water. 20 drops Fe, Cl, in 60 grms. water. mixture of 1 part A and 2 parts B. D = mixture of 1 part A and 1 part B. E = mixture of 2 parts A and 1 part B. F = 1 grm. FeO SO, in 60 grms. water. No. 20. Sensitizer S. Developer C. a clear dark lead colored print having No. 21. Sensitizer S. Developer D. a brown print with a shade of red. No. 22. Sensitizer S. Developer E. a reddish brown picture. No. 23. Sensitizer S. Developer, 1st, A; 2d, C. Exposed one minute-a black color nearly resembling nitrate of silver prints. In several trials a blue color predominated.

a

Exposed one minuteshade of blue. Exposed one minute

Exposed one minute;

No. 24. Sensitizer S. Developers A and FB. Exposed one minute. A clear greenish black picture.

The photographs enumerated above are but a small portion of those taken; some of the processes were repeated and only the best pictures retained. În describing them it is difficult to convey in words a correct idea of color, tone, intensity, clearness, &c. Inexperience in manipulation was often a cause of ill success.

No. 7 is a novelty; the chlorid of iron penetrates the paper where not reached by the light and the nutgalls bring out an ink negative. By comparing No. 8 and No. 9 we observe the superiority of glycerine. No 14 is a far better print than No. 13, which is taken by known methods. By modifying the strength of solutions A, B, C, D, E and F, and varying time of exposure and intensity of development a great variety of colors may be obtained; passing from brick red, through brown red, brown, black brown, green black, blue black to light blue, besides intermediate neutral tints. The color of nitrate of silver may be fairly imitated, but I candidly confess I have been unable to reproduce the delicacy of line, beauty of tone and finish characteristic of ordinary gold and silver prints.

New York, June, 1869.

* Ordinary commercial solution.

ART. XXIII.-Contributions to Chemistry from the Laboratory of the Lawrence Scientific School. No. 8.-On the action of the alkaline nitrites upon uric acid and its derivatives; by WOLCOTT GIBBS, M.D., Rumford Professor in Harvard University.

[Read before the National Academy of Sciences, April 15th, 1869.]

THE products of the action of nitrous acid upon the members of the uric acid group have been little examined. Baeyer has shown that hydurilic acid by the action of potassic nitrite yields alloxan and potassic violurate, the equation expressing the decomposition being as follows:

The nitrous acid in this case exerts an oxydizing action and is reduced to nitric oxyd. The action of nitrous acid upon urea has long been familiar to chemists, but, so far as I have been able to find, urea and hydurilic acid are the only members of the uric acid group the relations of which to the nitrites may be considered as known. I have undertaken in some measure at least to supply this deficiency in our knowledge and present the following as the result of my work.

Uric acid was diffused in cold water and a current of the red gas resulting from the action of nitric acid upon starch or sawdust passed into the liquid; effervescence almost at once commenced and after a time the acid was wholly dissolved. On evaporation the liquid yielded an abundance of yellowish crystals together with a small quantity of a brick red insoluble substance. The crystals were easily purified by solution, treatment with animal charcoal and recrystallization. They were then perfectly colorless, but became slightly pink on drying and possessed all the properties of parabanic acid. On analysis 10358 gr. gave 0.1790 gr. water and 1-2103 gr. carbonic acid, corresponding to 31.86 per cent of carbon and 1.91 per cent of hydrogen.

3 2 2 3

The formula €,H2N2, requires carbon 31 58, hydrogen 1.75; the substance analyzed was therefore parabanic acid. With ammonia it yielded ammonic oxalurate, easily recognized from its characteristic properties. The red matter mixed with the parabanic acid dissolved in a very large quantity of water to an orange yellow liquid which, on cooling, deposited a reddish flocky matter in quantity too small for analysis. The motherliquor of this substance fluoresced strongly with a blue color. In a second experiment alloxan and alloxantin were detected