604 REPORT— 1901. 



to diffused doyllght. The whole of the exposed surface was very dark in colour, 

 especially wliere the exposure was most complete. On examining it under the 

 microscope it was found to be covered with little granules varying in colour from 

 yellow to dark reddish-brown. Where the dark granules were thickest there were 

 found small yellow lumps that had all the appearance of colloidal matter. Some 

 of this was removed and treated with water, The microscope revealed a quantity 

 of light-coloured translucent films ; the edges of the drop of water on evaporation 

 showed imperfect colourless crystals resembling closely those obtained from other 

 specimens of tin colloid, together with gelatinous matter. It was evident that 

 there had been a slow chemical change, greatly due to the action of light, as 

 the back of the trade mark, which was practically in the dark, showed very little 

 discoloration. In order to see whether this could be repeated within a short time, 

 three experiments were made on freshly cut surfaces of tin. The tir.st was kept in 

 the dark for si.x weeks, and sometimes subjected to a temperature of 100° C. : 

 under the microscope it showed no clear sign of any action. The second w^as 

 exposed for the same time to diffused daylight : it showed slight but unmistakable 

 signs of granular formation. The third was exposed to direct sunlight : it was 

 distinctly spotted over with dark-coloured granules. 



2. Transitional Forms between Colloids and Crystalloids. 

 By Dr. J. H. Gladstonk, F.R.S., and Walter Hibbert, F.I.C. 



The investigation of the crust formed on the tin trade mark referred to in the 

 previous paper induced the authors to carry the inquiry further. Among tlie 

 remains of the ancient British village near Glastonbury, which had been 

 submerged in the marsh for 2,000 years, were the rod and weights of tin described 

 in the British Association Report for 1899, p. o95; and an examination of the 

 crust formed on these objects showed the gradual formation of yellow, amber, and 

 reddish-brown hydrates, together with minute egg-like bodies, which, when 

 broken, were found to contain gelatinous matter soluble in water, and giving on 

 evaporation crystals having curved edges. The crystals are very definite in form, 

 but are generally colourless and hygroscopic. A specimen of native cassiterite 

 gave similar results ; and so did colloidal tin hydrate formed from stannic chloride 

 by dialysis. Colloidal hydrate of titanium gave intermediate bodies closely 

 resembling those of tin. The same was found to be the case with aluminium and 

 palladium colloids. No similar forms have yet been obtained from silica ; but it is 

 well known that quartz crystals, diamonds, and ice are apt to exhibit curved edges 

 and coDchoidal fracture. 



The authors regard these semi-crystalline bodies as intermediate forms 

 betweeen the gelatinous colloids, whether pecti.sed or not, and the ordinary 

 crystallised metallic hydrates. They look upon them as consisting of the hydrate 

 combined with many molecules oi' water, and think that the various kinds of 

 crystals (crosses, fishes, rhombs, kc.) are due to different amounts of combined 

 water, as they show different degrees of solubility and of diffusibility. The 

 isomorphism between these hydrates of tin, titanium, and aluminium is worthy of 

 notice. 



The secular changes that take place in these gelatinous hydrates, and the 

 formation of the insoluble films, are the subject of investigation at the present time. 



3. Report on the Nature of Alloys. — See Reports, p. 75. 



4. The Minute Structure of Metals. By G. T. Beilby. 



Microscopic examination of metallic surfaces produced by breaking, tearing, or 

 filing, by rolling, drawing, hammering, or polishing, has shown that the metals as 

 they are ordinarily met with appear in two forms : — 



(n) As minute granules or scales. 



(A) As a transparent, glass-like substance. 



