168 PROF. W. J. SOLLAS ON A PROCESS FOR [May 1902, 
informed me, of kentallenite, a rock which has been described by 
Messrs. Hill & Kynaston.* In making my analysis I did not weigh 
the several components, having found that their relative proportions 
could be determined in most cases by bulk-measurements made in 
narrow graduated tubes. Subsequently I found that this process 
was inapplicable to rocks containing minerals like biotite, flat- 
leaved scales always packing after a law different from that for 
angular grains, and giving results which are always too high. Ihave 
no doubt, therefore, that somewhat too great a proportion of biotite 
appears in my results. The error introduced into volumetric mea- 
surement by the difference in the mode of packing of differently- 
shaped grains may be met by first placing benzol in the measuring- 
tube, and recording its displacement when the mineral is added; but 
this destroys the simplicity of volumetric estimation, so that no 
advantage is offered by it over the more exact method of weighing, 
which J now therefore always employ. 
The mineral composition of kentallenite was found to be as 
follows :— 
Sp. gr. Per cent. 
Soda-orthoclase (Ab, Or,) ............ 2°59 9°64 
MATIC ERINIG Ue 2.5), ac smudists > see essed Senet 7 2°67 25°15 
BLObiber ric. «tensbeees teeatbreeen sansa. 2°98 17-77 
Pyroxene (Oblique) | .a.<.1-s04-75q-re->: 3°20 15°92 
Pyroxene (rhombic) ”.... J... sass sass: 3°34 23°00 
SONG YAH eae 2 Pte haves oe ie dlekpe cence: 3°36 6:07 
INR OMITTED 65. cee ees tags nr cies dean: sje 2-45 
100-00 
From published analyses of similar minerals with similar specific 
gravities the chemical composition was calculated, with the results 
given in the first column of the following table; in the second 
column the results of direct chemical analysis, as communicated to 
me by Mr. Teall, are given for comparison. 
Ee II. 
SOA ar cet 2 ABR AAA 50:3 52°09 
BAIS, escent cnet 12°6 12:25 
MeO dine: oeeten. 2°6 1:84 
i It 6 I ea are croee 5:9 Taek 
OL 0 enema rE ay 6 10:7 7°84 
1. 1 ed 0 ie ne-yo 11°9 12°48 
ROO). a. Sn 21 301 
Na OF ai ee 2-9 2°04 
LSC) | sateen ca ee 0-6 O51 
ALO FARES or teehee ae 0-4 0°73 
PO Focus gi seeeee 0:3 0-34 
100°3 100°24 
—— a 
On my informing Mr. Harker of the results of the examination 
of the two specimens which he had sent me from Skye, he tabulated 
them along with the results of their chemical analysis, as made by 
Dr. W. Pollard, in parallel columns as shown on the next page :—- 
1 Quart. Journ. Geol. Soe. vol, lvi (1900) p. 537. 
