i873-] Comparative Vegetable Chromatology. 451 



0*6095 grm.: when withdrawn from the crucible it had 

 become quite dull, with the exception of two facets which 

 had preserved their brilliancy, but were tinged with iri- 

 descent colours ; the carbonic acid current had exerted 

 upon them a comparative cooling action ; the stone had 

 lost about 2 milligrammes. This proves that the 

 diamond is capable at a white heat of decomposing car- 

 bonic acid, and of combining with its oxygen, but the 

 action is very slow. This decomposition had already been 

 perceived by M. Jacquelain, although his mode of operation 

 was uncertain in his results. A receiver was employed with 

 two openings, and filled with carbonic acid ; one opening 

 communicated with a tube, at whose extremity the oxy- 

 hydrogen gas was burnt ; through the other was introduced 

 the diamond supported on a piece of pipe-clay. In this 

 experiment the diamond was consumed rapidly, but espe- 

 cially by the oxygen of the oxyhydrogen mixture, no trace 

 of blackening being perceptible. 



III. ON COMPARATIVE VEGETABLE 



CHROMATOLOGY. 



By H. C. Sorby, F.R.S., &c. 



tN an article on the various tints of autumnal foliage, 

 published in this journal for January, 1871,* I 

 described a number of the leading kinds of colouring 

 matters found in the higher classes of plants. Since then 

 I have studied them far more thoroughly ; so that what 

 I said must be looked upon as a mere commencement of a 

 subject: which has now become so extensive, and includes 

 special modifications of so many branches of science, that 

 it appears desirable to give some single name to the whole. 

 It is for this reason that I have called it chromatology. In 

 this former paper my chief object: was to describe the cause 

 of the production of the various tints of leaves when they 

 fade. This is mainly the result of chemical changes taking 

 place when the leaves are dying or dead, which correspond 

 very closely with what can be imitated artificially by acting 

 with various reagents on the dead materials extracted from 

 the living plants. On the contrary, my object now is to 



* New Series, vol. i., p. 64. 



