NOTES AND QUERIES. 



151 



similarly in the Isle of Lemnos, and at Magnesia, in Asia Minor. It is 

 there associated with magnetic iron or crystallized magnetite. It occurs 

 along with diaspore in the dolomite of St. Gothard. It occurs near 

 Ephesus, and also in the Isle of Naxos, in the same way. Here are five 

 specimens of corundum in its opaque, common form. In its finely-divided 

 state it is commonly known as emery, which is nothing more than the com- 

 mon form of the true sapphire. Some of the analyses of this substance 

 give water as an essential constituent, but the sapphire and the ruby are 

 nothing more than crystallized alumina without water. But there are 

 analyses of some two or three specimens of corundum in which we find 

 water given as a constituent. An analysis of corundum from Asia Minor 

 gives 37 per cent, of water, and an analysis of corundum from India 

 gives 3*1 per cent, of water. In these cases, probably, they contained 

 diaspore associated with them. There is a difficulty in many of these 

 analyses, and we cannot extract rational formula? of the results obtained 

 by approximate analysis, because these crystals have the power of enclosing 

 within their mass a very large amount of matter which in no way enters 

 into the chemical composition of the mineral itself. It is there as so much 

 foreign matter entangled in the crystal, and yet the crystal shall have a 

 definite form, and so forth. There is a portion of matter which we must 

 not take cognizance of, but we have no means of separating it mechani- 

 cally from the mass. It all comes into our results, as we have no way of 

 separating this dirt, as metallurgists call it. 



Now for some examples of the so-called aluminates. There is a form of 

 ruby which is an aluminate of magnesia. It is coloured a fine rich 

 colour, apparently with chromate of potash ; but of course it is not equal 

 to the oriental ruby. It consists of one equivalent of magnesia and one 

 of alumina. Its formula is, MgOAl 2 0 3 , so that you see that the alumina 

 contains three times as much oxygen as the magnesia. It may be obtained 

 beautifully crystallized, and was so obtained by Ebelmen. It is made 

 simply by heating magnesia and alumina with fused boracic acid, with 

 the addition of a little chromate of potash. The experiment was made 

 in exactly the same way as that with reference to the crystallized alumina 

 prepared in the porcelain furnace at Sevres, near Paris, already spoken 

 of. Ebelmen obtained in this way distinct crystals of aluminate of mag- 

 nesia, having a fine ruby-red colour. The} 7 are exceedingly small, but 

 they are, nevertheless, instructive, small though they be. Then, by 

 adding a little cobalt, he obtained crystals of the same form, having the 

 characteristic and beautiful blue colour of the natural mineral. 



NOTES AND QUERIES. 



Typical Mammalia in British Museum. — Dear Sir, — Allow me to 

 point out to you an omission in your list of figured specimens of fossil 

 mammalia in the British Museum ('Geologist,' March, 1864). I have 

 lately described and figured, under the name of Hyana antiqua (Annals 

 and Mag. of Nat. History, January), a molar tooth from the lied Crag of 

 Suffolk, which is now in the national collection. As this announcement 

 may stimulate others to search in the same direction, I trust you will in- 

 sert it in your journal. — Truly yours, E. Ray Lankester. 



8, Savile Roto* W. 



