868 



Just because neither we, nor our predecessoi's, ever found any 

 indication of another form of the metasilicate, than the mentioned 

 biaxial one, we wrote to Mr. Fkiedel, asking him to send us a 

 sample of his modification. We wish to offer this mineralogist our 

 best thanks once more, for his aid and the trouble he has given 

 himself, to help to elucidate the complicated problem of those form- 

 deviations. 



The preparation sent to us, soon appeared to be an aggregation 

 of flat needles, often radiail)^ ordered, loJiich. were however duuhtles.s 

 hlaxial. As was indicated on (he label, they were obtained from 

 molten LICI, showed a pale pijik tinge, and an extinction, directed 

 perpendicularl}' and parallel to their elongation ; the refraciive index 

 for vibrations parallel to their dii-ection of elongation, was: 

 njj = 1,585 + 0,003, (being thus identical with that of our needles, per- 

 pendicularly to their elojigatioii), while the refractive index for vibrations 

 orientated perpendicularly to the above, was: /z^; =z 1,563 + 0,002, 

 from which there results a birefringence of about : 0,022, being thus only 

 sH"htly less than for puie metasilicate. The flat needles showed at 

 their to})-, and base-cud, two small faces, making with the longer 

 edge of the crystals angles of respectively : 114°. 126°, and 120°. 



In an experiment, where finely (^rushed Li^>Si O ^ was healed during 

 eif^ht hours with molten Li(J at 900° C. no other ci'ystals were 

 obtained than the oidinary. I)ia>:ial needle-shaped form, which we 

 described already. 



For another preparation of Mr. Frikdel, (wiih the number IVj, also 

 obtained from mollen LiCL which preparation contained some metallic 

 copper M, and some LiCl, we found : ilj = 1.584 ± 0.002, and 

 njj = 1.574 =b 0.002, the directions of the vibrations corresponding 

 with those, given earlier. The birefringence is thus now : 0.010 or 

 0.012 ; evidently the refractive index for vibrations in the elongation- 

 direction of the needles, seems to be variable. We think it not im- 

 probable, that a slight admixture in solid solution, of the bisilicate : 

 Li^Si^Ch with its lower refractive index : ca 1.54, must be supposed, 

 to be the cause of this variability. 



^ 8. After having received the account of these experiments, Mr. 

 Friedel was so kind as to repeat his experiments of 1901. Further 

 he succeeded in finding again a preparation o'" llie year 1898 (C ; 

 exp. 1, 1898), prepared by heating a solution of 2,5 grams of dried 

 SiO.^ and 0.65 gram of LLO, with 6 grams of muscovite at 540° C. 



') From the lining of the steelbomb, used in this and other experiments. 



