90 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



by Crooks in 1871, as the result of spectral analysis that, if 

 procurable in sufficient quantity, it promises to be of great 

 value for the production of colors ; as many beautiful sjjeci- 

 mens of yellow and orange-red, which are chromates of thal- 

 lium, and green, also a chvomate, and a dark brown, which is 

 a sulphuret of the metal, were exhibited by Messrs. Winsor 

 and Newton, the eminent colorists, of London. 4 B, Sept., 

 1871,675; do. Oct., 1871, 745. 



ACTION OF LIGHT ON OLIVE - OIL. 



Olive-oil, in its natural state, contains in solution a yellow- 

 ish substance, which, when the oil is treated with acids or 

 with caustic soda, gives rise to the well known greenish col- 

 oration. By exposure to sunshine this coloring matter is es- 

 sentially altered, the oil being thereby decolorized, and no 

 longer exhibiting a greenish color when treated with the re- 

 agents above mentioned. Moreover, other changes take place 

 at the same time in the constituents of the oil, the olein in 

 particular being greatly altered, and acquiring the fundamen- 

 tal property of elaidin, namely, that of not solidifying in con- 

 tact with nitrate of mercury mixed with nitrous products ; 

 at the same time free acids are formed, and the oil acquires 

 a rancid taste and odor. 21 A, Dec, 1871, 1192. 



CHEMICAL INTENSITY OF TOTAL DAYLIGHT. 



Messrs. Roscoe and Thorpe, in a paper upon the chemical 

 intensity of total daylight, as observed at Catania during the 

 eclipse of 1870, remark that, for the purpose of determining 

 the variation in chemical intensity caused by the alteration 

 in the sun's altitude, observations were made on the three 

 previous days, and that the results obtained confirmed the 

 conclusions formerly arrived at, " that the relation between 

 the total chemical intensity and sun's altitude is represented 

 by a straight line." It was difficult to estimate the chemical 

 intensity of the feebly diffused light during totality, owing 

 to the obscuration of the sun's disk, and to the greater part 

 of the heavens being covered by clouds. Not the slightest 

 action could be detected after an exposure of the sensitive 

 paper for ninety-five seconds. It was estimated that the 

 chemically active light present was certainly not more than 

 0.003 of the unit adopted, probably much less. 



