740 Geological Society : — 



Uookham's Crystals. 



Another remarkable example of fine periodic structure 

 was brought to my notice by Mr. George Hookham. In 

 this case double retraction plays an important part and a 

 careful study o£ the crystals requires the use of a polarizing 

 microscope. I have had the advantage not only of receiving- 

 interesting specimens and a sample of one of the solutions 

 employed, but also of witnessing for myself Mr. Hookham's 

 procedure. 



The active ingredient is copper sulphate ; but, as it is 

 desired to obtain a film which is initially amorphous, other 

 ingredients must be added. In the solution given me there 

 is both salycine and sugar. Mr. Hookham describes it as 

 consisting of a solution saturated (in the cold) with copper 

 sulphate and salycine, to which is added 3 per cent, of 

 strong syrup. A few drops are placed upon a strip of 

 glass, such as are ordinarily used for microscopic slides, 

 and are spread with the finger. The slide is then warmed 

 over a spirit lamp, when any excess of liquid may be 

 thrown off. By a further application of heat the whole 

 is then dried somewhat rapidly. There is usually immediate 

 formation of crystals at the edges, but throughout a space 

 in the interior the film should be amorphous and nearly 

 invisible. At this stage the amorphous film shows nothing 

 in the polariscope, but in a short time after cooling deve- 

 lopments set in and proceed with rapidity. There is much 

 here to excite admiration and perplexity, as in other similar 

 phenomena of crystallization, but the feature in which I 

 am specially interested, viz. the formation of a structure 

 periodic several thousand times in the inch, does nor appear 

 to present itself unless the plate is kept warm until crystal- 

 lization has set in. Mr. Hookham mentions a temperature 

 about 30° F. above that of the room. I have usually placed 

 the slides over hot water pipes or on the mantelpiece. 



LXXIX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 668.] 



May 7th, 1919.— Mr. GL W. Lamplugh, E.E.S., President, 

 in the Chair. 

 HP HE President said : — Major E. W. Brock, formerly Director 

 -*■ of the Geological Survey of Canada, was called upon last year 

 to undertake on behalf of the War Office an arduous journey in 

 Palestine, during which he had to devote particular attention to 



