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1 



Foiu'th Supplement to Donas Mineralogy. 131 



Ytirotawtalite fp. S59]. — Tliis Ytterby mineral contains, according to C. F, 

 Chandler, (Inaug. Dissert.) ; 



7a 57-27, W I'So, Sn 0*10, Ca 4*78, % 0*75, tTS'lO, f'e 4*82, Y 18-64, 6u0-69, 

 S with a trace of sulphur 6-00=100. Or, excluding the water, Ta 60-91, W 1-97, 

 Sn O-ll, Ca 5-09, 3Ig 080, tF 5-42, f^e 5'13, Y 19'84, Cu 0-73=100. 



Zircon [p. 195]. — In the collection of the Ecole des Mines, there are two crystals 

 of zircon iVom Brazil (Serro de Frio) which have the pyramidal terminations trun- 

 cated, and in one this flat terminal or basal plane is very large. G.=4-47 — 4-41. 

 Mr. Friedel, Ann. des Mines, [5], ix, 629, 1856. 



Tlie zircon of Buncombe Co., North Carolina, contains, according to C. F. Chandler 

 (Inaugf. Dissert., Gott. 1856): 



Si 33-70 2r 65-30 3Pe 0'67 fi 041 = 100-08 



G. of four crystals, 4-555, 4-578. 4-594, 4607 : the same after ignition, 4*672, 4-661, 

 4'631, 4'650; loss by ignition, 0397 to 0449 p. c. 



ADDENDUM, 



ALLoniAKE. — The allophane of New Charlton, near Woolwich, has been analyzed 

 by A. R Northcote, with the following results (Phil. Mag., [4], xiii, 338): 



gi ^1 ' Fe Ca ft C 



1. Amber-like varietv, 20-50 3134 O'Sl 1*92 4291 2-73= 99-71 



2, Scnii-opaque, friafile, 19*53 37-30 0-11 1*36 39*19 2*44= 99-98 



3, Ibid, 17-00 39*09 trace 1-50 40*92 1*49 = 100 



4. Riby-red, transparent, 1705 3288 Fe 659 1-34 40'31 1-82= 99*99 



Excluding the carbonic acid, lime and protoxyd of iron, the oxygen ratio for Si, S, 

 fi, is as follows: 



(I) 1 : 1-37 : 358 (2) 1 : l'7l : 3-42 (3) 1 : 206 : 4'll (4) 1 : 1*96 : 4 



At 100*^ C. the loss of water in (1) 27*11, or over 3-5ths of the whole; in (2) 

 20-76; in (3) 20*10; in (4) 21*97 ; in the last three about half the whole amount of 

 water. Supposing this water non-essential, the ratios ^become : 



(1) I : 1*37 : 1-32 (2) 1 : 1-71 : 1-61 (3) 1 : 2*06 : 209 (4) 1 : 1*96 : 1-84. 



Mr. Northcote excludes still farther,-^as required by his idea of the formula, — from 

 (I), t\ti out of lUft; from (2), 2fi out of 14ft; from (3), 3fl out of ISfl-; from 

 (4), lit out of 13ii;* and thence has the formulas as follows: 



(I) *lSi3-[-3Sllj[^ (2) 3tlSi»-i-4Slfl3 



(3) 5lSi«+63tlS' (4) ilSi'+4(Xl.Fe)lI5 



making them compounds of an unknown silicate and Gibbsite in different pro- 



portions. 



[This second deduction of water, reduces the several oxygen ratios to 1 : l'37:l-04 

 1 : 1-71 : 1-48, 1 : 206 : 1*74, 1 : 1-96 : 1*71. 



There is so much that is arbitrary in the assumption of 100^ C. a? the dividing 

 temperature between the stable and unstable water in such hydrates, and also in 

 the rejection of -j-^^th to ^th of the water beyond this, for the sake of a formula, 



that, for the present, the mere oxygen ratios for given temperatures best represent 

 our actual knowledge, and especially as allophane is an amorphous mineral. If a se- 

 ries of experiments were made for successive temperatures from 40° C. to 120° C, (or 

 beyond), and at some point in the h"nc, an abrupt diminution of the water eliminated 

 were found, then one step would be taken towiirds the discovery of the temperature 



* It is difficult to understand how this water here cut off can be regarded as " hav- 

 ing probably crept in as an erroneous result " especially as 20 per cent or more of 

 water were before excluded. 



