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 
tap 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 illustrati ig the mine 
talogical survey of the environs of Paris, made by Messrs. 
Cuvier and Brongniart; they are particu le i 
that connexion, and especially as giving precise ideas of the 
ignification 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, &c. 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 
It. 
In justice to the numerous contributors to this work, we 
feel authorized to publish the following remarks upon the 
merican Journal, which if it were exclusively or even prin- 
