NON-OXYGENATION OF PHOSPHOR I 18. 



being th of an inch ; the outer limb was fitted with a scale. After having opened the* 

 cock, a, a stick of dry phosphorus, e, was suspended in the cylinder, which was made 1 

 very clean and dry, and the siphon being filled with water, was firmly seated in its 

 place and the cock closed. Now, as the phosphorus oxydized, the metaphosphoric 

 acid was removed by the water present, and the level falling in the lateral limb, indi-> 

 cated what quantity of oxygen was consumed, and, therefore, the rate of combustion 

 of the phosphorus. This was expected to give a more accurate estimate of any chan- 

 ges occurring in the phenomenon, and was accordingly applied to detect them. 



441. Beams of light of different colours being made to pass at different times through 

 the cylinder, so as to impinge on the phosphorus, attempts were made to ascertain the 

 rate of combustion for each, as also for the white light of the sun, and in the shade. 

 In each insulated experiment, the fluid in the gauge sunk with great regularity, more 

 rapidly at first, and then more slowly, but the same regularity was not observed in dif- 

 ferent trials. At one time the phosphorus would consume with more than double the 

 rapidity than it did at another, though to all appearance under identical circumstances. 

 If the slow combustion of phosphorus be at all affected by the action of solar light, it 

 is certainly not to that extent which Ritter supposed. So far from extinguishing, the 

 violet rays do not exert any control over it, or if they do, it is to so small an extent 

 that the most delicate arrangements fail to detect it. 



442. It is possible, however, that atmospheric temperature may exert an influence 

 on the result. During the trials here made, a thermometer in the shade ranged from 

 70 Fah. to 82 Fah. At these points the affinity of the combustible material for oxy- 

 gen may be so exalted that the action of any weaker force becomes masked. It is not 

 stated what were the temperatures at which the alleged results were obtained. But it 

 is most probable that the presence of extraneous matter was the cause of all these vari- 

 ations. It is well known that certain compounds of hydrogen and carbon, in ex- 

 tremely minute quantity, will entirely put a stop to the oxydation of phosphorus ; and 

 during the course of these trials, I have had abundant reason to notice errors arising 

 from this cause. By simply wiping out the cylinder with a linen cloth, which con- 

 tained an almost imperceptible trace of spirits of turpentine, an erroneous result like 

 that of Ritter was at once obtained. 



443. DECOMPOSITION OF THE SALTS OF SILVER. Several of the salts of silver un- 

 dergo a remarkable change when exposed to the rays of light, the bromide, the 

 chloride, and the nitrate being very good examples; these, which are all white, become 

 of a dark colour, approaching almost to black, when exposed to the violet rays ; it is 

 stated that the bromide is most readily affected, yielding a brownish-black colour. 



444. If a piece of paper be soaked in a solution of nitrate of silver, and then dipped 

 into a solution of bromide of potassium, it affords a very advantageous means of ma- 

 king these experiments. The chloride may occasionally be substituted for the bromide 

 of silver. 



445. A beam of light (Jig. 65, a a) entered a dark chamber horizontally, and was 

 obstructed in its course by a plane metallic screen, b, having a hole half an inch in 

 diameter in it. The beam, c, which passed through this aperture fell upon a flint 



