Imperial Institute of France. 69 



weak with respect to the juice obtained by expression, and 

 four times weaker in the extract from the leaves and stalks : ' 

 the first only has the pecidiar odour on which the bad 

 cfTccts of opium are thought to depend. 



M. Chevreul, assistant at the Museum of Natural History, 

 has made experiments upon pastil, with a view to illustrate 

 its effects as a substitute for indigo ; or rather, he has made 

 this interesting plant the object of researches still more 

 general, and belter adapted for perfecting all the methods of 

 vegetable analysis. He has shown that the feculum of the 

 pastil is composed of wax, and of a combination of greea 

 resin, of a vegeto-animal matter, and of an indigo in the 

 state of deoxidation, but which may easily again take back 

 its oxygen. The filtered juice has also furnished him with 

 substances the number and variety of which are astonish- 

 ing, and from which we may conclude, that some of those 

 which we have hitherto regarded as the immediate princi- 

 ples of vegetables, may he divided without decompositiou 

 into more simple principles. 



The same chemist has presented a similar series of ex- 

 periments on Campeachy wood. He has discovered in it 

 fifteen different principles, tbe most remarkable of which 

 is that which he has called campechium, and to which this 

 wood owes its dyeing properties. This principle is a red- 

 dish brown, without taste or smell ; it crystallizes ; gives 

 out upon being distilled the same elements with ani- 

 mal substances ; is combined with all the acids and all the 

 Salifiable bases j and forms with the first of these substances 

 red or yellow conibinaiions, according to the quantity of 

 acid emploved, and with the others violet blue combina- 

 tions ; anfl that with the more facility, as we may employ 

 it with more safety than the syrup of violets, in order to 

 find Out the alkalis; but the oxirle of tin at the maximum 

 forms an exception to this rule. It acts upon campechium 

 like an acid, and reddens it; whereas the sulphuretted hy- 

 drogen, which under other circumstances acts like the 

 acids, takes the coloiir from campechium. 



Hitherto the theory (^f affinities had been applied only 

 to the reciprocal decompositi()n of the soluble salts: it re- 

 mained to be seen, if tiie insf)liible salts were also suscepti- 

 ble of changinir principles with certain soluble salts. 



M. Dulong has examined this question in a general 

 manner, in a memoir presented to the Class, and which is 

 the tirst production o\ this voung chemist. He first treats 

 in particular of the action of the carbonates and of the sub- 

 tarbonalcs of potash and soda on all the insoluble salts, 

 E 3 ml 



