218 Letters of Mr. Brongniart, with remarks. 



ing to the letter, we will add (a fact that appears not to be 

 generally known in this country,) namely, that the steel lustre 

 on porcelain is metallic platina, and that the copper lustre is 

 metallic gold to which this particular tinge is imparted by 

 an umber basis below — the gold being partially pervious to 

 light and the only metal that is so. It is sufficiently curious 

 that the gold is applied to the porcelain in the condition of 

 fulminating oxid ; the oil of spike is used to make it adhere, 

 and the fulminating properties are gradually destroyed with- 

 out an explosion.* 



The time will arrive, when the manufacture of porcelain 

 will become a great object in this country, and we cannot be 

 too early in acquiring the requisite information. 



Mr. Brongniart goes on to mention, 



" 2. Some minerals and rocks from the environs of Paris 

 and from France, and even from foreign countries, which 

 (he adds) I hope will be interesting to you." 



Among these specimens are many illustrating the mine- 

 ralogical survey of the environs of Paris, made by Messrs. 

 Cuvier and Brongniart; they are particularly valuable in 

 that connexion, and especially as giving precise ideas of the 

 signification of the terms used by those gentlemen. 



"3. Distinct copies of some of Mr. Brongniarts works — 

 he observes, 



" I would also have added a copy of my essay upon the 

 classification of mixed rocks, published in 1813, he. but I 

 have only one perfect copy. Besides, I have since that pe- 

 riod made many changes in this classification, and I intend, 

 as soon as possible to publish a new and much more com- 

 plete edition than the first." 



This remark is cited that Geologists may avail themselves 

 of Mr. Brongniart's aid, as soon as his new edition shall ap- 

 pear; we shall not fail to give our readers the earliest notice 

 of it. 



In justice to the numerous contributors to this work, we 

 feel authorized to pubhsh the following remarks upon the 

 American Journal, which if it were exclusively or even prin- 

 cipally our own production, we should of course suppress. 



"I have received sir, and I continue to receive, with regular- 

 ity, your Journal of Science and Arts, and I return you my par-- 



* A private communication from London to the Editor. 



