Notices respectiiig New Books, 225 



that the sulphuric acid destroys the gum, the mucilage, the sugar, 

 &c., and leaves the colouring matter unaffected ; hence the greater 

 beauty of garancine colours. To account for the greater proportional 

 effect of garancine, it has been said that a part of the colouring mat- 

 ter is enclosed in cells of the wood, so that it cannot be dissolved by 

 water, and that the sulphuric acid destroys the wood and liberates 

 the colouring matter. To these views it may be objected, that con- 

 centrated sulphuric acid, though it does not affect alizarine, does not 

 destroy any of the injurious substances in the root except the xan- 

 thine, while the rubiacine, the resins, and the pectic acid, escape 

 its action : and as far as the wood is concerned, I can affirm that 

 the operation succeeds equally well if acid be taken of such dilution 

 as not to destroy woody fibre. I think that the superiority of garan- 

 cine can only be attributed to two causes. In the first place, since, 

 as I have shown above, there is a quantity of colouring matter in 

 the root combined with lime and magnesia, by which it is rendered 

 insoluble and incapable of dyeing, one effectof the acidis to remove 

 this lime and magnesia, and to set the alizarine at liberty, which is 

 then capable of application. In the second place, the xanthine, 

 which has an injurious effect in madder-dyeing, is removed by 

 washing with cold water, since it is not precipitated by acids, while 

 the whole of the alizarine remains. If hot acid is employed, then 

 the xanthine, or a part of it, is converted into that dark green sub- 

 stance which I have mentioned above as the product of the action 

 of muriatic and sulphuric acid on xanthine ; hence the dark colour of 

 garancine, which is not owing to the charring of the woody fibre, as 

 sometimes asserted. It must be remembered however that the ru- 

 biacine, the resins and tTie pectic acid, as well as the alizarine, remain 

 uncombined after treatment with acid. Hence it becomes necessary 

 to add some base with which these substances may combine, so as 

 not to interfere with the action of the alizarine. I believe it is the 

 practice of garancine manufacturers to employ soda for this purpose. 

 I think it would be better to use a small quantity of lime-water. 



I may state in conclusion that the experiments described in this 

 and the last report were made with Avignon madder. The con- 

 stituents and properties of Dutch madder, which is of rather a dif- 

 ferent nature, remain to be examined. 



I have been lately engaged in examining the colouring matter of 

 fustic, which I have prepared in a state of purity, but the investiga- 

 tion is not sufficiently advanced to justify me in making known the 

 results on the present occasion. 



XXIX. Notices respecting New Books. 



Introduction to Meteorology. By David Purdie Thompson, M.D. 

 Blackwood and Sons. 



n|"'HERE is no branch of physical science which has made so little 

 -■• progress, and of whose laws our knowledge is so limited, as 

 that of Meteorology. Hence every encouragement should be given 

 Phil. Mag. S. 3. Vol. 35. No. 235. Sept. 184.9. Q 



