28 Allen, etc. — Diopside and its Relations 



We made a number of experiments witli the intention of 

 finding whether the mix-crystals of diopside and magnesium 

 silicate could be crystallized again from calcium chloride, or if 

 not, what change in composition they would show with varying 

 quantities of the chloride, but the products obtained were not 

 only not homogeneous, but the crystals were too small to sepa- 

 rate from one another and the microscope was unable to 

 identify them. One difficulty in these experiments was the 

 impossibility of entirely excluding water from the apparatus. 

 Its reaction with the calcium chloride, of course, formed some 

 free lime, which was dissolved by the silicate. Pure diopside, 

 as we have seen, does not dissolve lime, but magnesium silicate 

 does. Three grams of the latter, containing only 0*12 per cent 

 of lime, was crystallized* from calcium chloride and analyzed 

 after the excess of the reagent was removed. It now contained 

 3*04 per cent of lime, an increase of 2*92 per cent. 



Part II. Optical Study, by Feed. Eugene Weight and 

 Espee S. Laesen. 



In the foregoing pages the theoretical aspects of the Ca-Mg- 

 metasilicate problem have been treated at length, evidence 

 from all sources, chemical, physical, optical and crystallo- 

 graphic, having been brought to bear on its solution. In this 

 general presentation of the problem, however, only the more 

 important and decisive optical and crystallographic data have 

 been made use of, their detailed tabulation having been 

 reserved for a separate section. In the following paragraphs 

 those details which are still lacking are listed, and in order to 

 avoid repetition, general theoretical considerations have been 

 avoided so far as possible. In the attack on the present prob- 

 lem the effort has been made from the very first to combine 

 the evidence from all viewpoints and to test each conclusion 

 by such evidence. It has been found that by this method the 

 constant interchange of ideas and the discussion of the details 

 of the problem have tended greatly to improve and to 

 strengthen the final result. 



For the sake of convenience the optical and crystallographic 

 features of the three compounds of this series will be considered 

 first, after which will follow the particular features of the 

 intermediate preparations. 



Calcium Metasilicate. — The two enantiotropic forms of 

 this compound, wollastonite and pseudo-wollastonite, have 

 already been described in detail in this Journalf and the 

 evidence need not be repeated at this point. Since the publi- 



* The crystals were small but well-developed. 

 f This Journal, xxi, 103-108, 1906. 



