September 28, 191 1] 



NATURE 



437 



general theory of colloids was given by Pr. H. Freundlich, 

 of Leipzig. Colloidal solutions stand between the two 

 of true solutions and coarse suspension, such as 

 Brmed by very sparingly soluble substances which do not 

 react with the solvent. Colloidal metals, sulphides and 

 - are termed " suspension " colloids or lyophobic 

 , mic colloids, which approach more nearly to the 

 true solutions, are lyophilic sols, or " emulsion " colloids. 

 In the coagulation of suspension colloids the electric charge 

 is of importance, and the addition of an electrolyte, by 

 ing the panicles, facilitates coagulation. In the 

 case of emulsion colloids, the individual characters of the 

 substances concerned are the determining factors, electrical 

 conditions being of far less importance. An account was 

 given of the phenomena of adsorption, which the author is 

 inclined to regard as an effect of surface condensation. 

 Finallv attention was directed to the bearing of colloid 

 chemistry in a number of directions. A very full discussion 

 followed, in which Sir Wm. Ramsay, Prof. Martin, Prof. 

 Trenton, and others took part. 



The ensuing paper by Dr. Barger dealt specially with 

 some applications of colloidal chemistry and its theories to 

 pharmacology. In a second paper Dr. Barger gave an 

 account of the adsorption of iodine by the glucoside 

 sapon.arin, which, on account of its being a pure substance 

 of definite composition and molecular weight, affords a 

 more favourable instance than starch for the study of the 

 iodine colouration. 



The colloid theory of cements was the subject of a very 

 lucid paper by Dr. C. H. Desch. The explanation of the 

 setting of calcareous cements, as caused by the crystallisa- 

 tion of the products of hydrolysis from a supersaturated 

 solution, fails to account for the great mechanical strength 

 of such cements. The colloid hypothesis proposed by 

 Michaelis attributes the setting to the formation of a gel 

 of calcium silicate, which subsequently hardens by loss of 

 water and adsorption of lime. Microscopical examination 

 confirms Michaelis's view. The only constituent of the 

 cement which is acted on is the alite. The hydrolysis of 

 the complex substances contained in the alite first sets free 

 calcium aluminate, which separates in the form of crystals. 

 This constitutes the initial set. The calcium silicate is 

 more slowly hydrolysed, and the calcium monosilicate 

 produced, being extremely insoluble, separates as a colloidal 

 gel. A part of the calcium hydroxide liberated crystallises 

 in large plates, and is readilv detected by the microscope, 

 whilst another part is adsorbed by the silicate gel. The 

 graaual increase of strength which is characteristic of 

 calcareous cements is a consequence of the continued 

 adsorption, and of the physical changes in the structure 

 of the gel. 



The colloids formed may be examined and characterised 

 by staining with dyes, such as methylene blue, patent blue, 

 and safranin. The principal difficulty in the microscopical 

 examination of cements has hitherto been the brittleness 

 of the material, making it impossible to grind very thin 

 sections, resulting in loss of clearness. This may be 

 nroided by treating the cement as a metallographic speci- 

 men, -rinding and polishing one surface onlv, and 

 examining under vertical illumination after etching with 

 weak acids or staining with other reagents. 



A brief paper on the rate of coagulation of colloidal 

 copper, by Mr. H. H. Paine, described the preparation of 

 the solutions and their coagulation by simple salts ; there 

 is an initial period during which the solution remains 

 clear. The rate of precipitation is proportional to the 

 square of the initial concentration of the colloid : for 

 varying amounts of the electrolyte the rate of coagulation 

 is proportional to some power of the concentration of the 

 salt. 



Reports were presented by all the sectional committees, 

 and a new committee was appointed bv the section for the 

 study of plant enzymes, with Mr. A. D. Hall as chairman 

 and Dr. E. F. Armstrong as secretary. Dr. Orton 

 reported on the transformation of chloro- and bromo-amines 

 into halogen anilides, on the velocity of chlorination of 

 anilides, and on the formation of nitroamines. The 

 attention of the Electroanalysis Committee has been 

 directed during the past year particularly to the application 

 of the electromctric method to the titration of weak acids 

 in such liquids as tan liquors. 



NO. 2187, VOL. 8-1 



GEOLOGY AT THE BRITISH ASSOCIATION. 

 PHE proceedings of Section C (Geology) were not 

 mark, d b\ am epoch-making paper, but a number of 

 subjects ol geological nterest were dealt with. On Thurs- 

 day (August 31) the section opened with the- address of 

 the president (Mr. A. Marker, F.R.S.), which was a 

 scholarly and stimulating treatment of some aspects of 

 modern petrology, in which the arguments of his treatise 

 on " The Natural History of Igneous Rocks " were 

 followed to further conclusions on the conditions of their 

 distribution and genesis. 



Of those who did yeoman service to the section, Mr. 

 Clement Reid, F.R.S., came easily first, his intimate 

 knowledge of the locality being freely drawn upon at two 

 meetings, and a third being made notable by a masterly 

 paper on the relations of the Glacial period to the plant 

 population of the British Isles. 



Following the president's address came Mr. Reid's paper 

 on the local geology. Portsmouth, he pointed out, was 

 the centre of geological features of considerable interest, in 

 which the student was brought face to face with many 

 difficult problems. The geological map showed bands of 

 colour ranging east and west, which in a flat country 

 indicated inclined strata having a well-marked strike, and 

 Portsmouth was near the central axis of the Hampshire 

 Basin. It was also close to one of the subsidiary ripples 

 on the great earth-wave, which formed Portsdown Hill. 

 The Hampshire Basin was a great synclinal fold, and the 

 planing of this fold by river and sea rendered visible 6000 

 feet of strata within short distance of Portsmouth. The 

 oldest rocks seen on the surface were the Wealden and 

 Lower Cretaceous beds of the Isle of Wight. The Chalk 

 which forms all the higher hills may be taken as a 

 foundation, as it is the oldest formation which plays any 

 obvious part in the geology of Portsmouth. The upper 

 zones had been carved away before the deposition of the 

 Lower Tertiaries, and much of the Lower Eocene was 

 also missing. The lowest brackish-water clays have 

 yielded no fossils near Portsmouth, but the London Clay 

 includes an irregular, siliceous bed (Bognor Rock) which 

 is very fossiliferous. Succeeding these come the Lower 

 Bagshot beds, which are poorly displayed near Portsmouth, 

 but thicken out at Alum Bay into a mass of current- 

 bedded sands in which occur beds of lignite and lenticles 

 of pipe-clay containing leaves of tropical plants. These 

 sands pass up imperceptibly into the marine Bracklesham 

 beds, which contain many drifted plants, and include a 

 prolific marine fauna of tropical appearance. Following 

 in regular succession comes the deeper water Barton Clay 

 with its great variety of beautifully preserved Mollusca, 

 followed by the Barton Sands, at the top of which it has 

 been the custom in England to draw the line between the 

 Eocene and Oligocene formations, because the succeeding 

 strata are markedly different in character, and the junc- 

 tion is rendered conspicuous bv an underclay and a swampy 

 land-surface ; but the line of demarcation is now drawn 

 higher up to suit the general European classification. 

 The Fluvio-marine series of the Isle of Wight and the 

 New Forest form a well-marked natural group of strata 

 consisting in the main of mottled clays and silts of 

 lagoon and brackish-water origin, with subordinate bands 

 of white tufaceous limestone and marl. Bands of marine 

 origin are quite subordinate except at the top. The 

 occurrence of scattered angular chalk flints at various 

 levels seems to point to the proximity of dry land against 

 which the strata abutted. The Fluvio-marine series carries 

 the succession up to the Middle Oligocene. All tin 1 higher 

 Tertiary strata have been destroyed, and the next deposit 

 is of Pleistocene date. 



The remarkable folds which have affected all the strata 

 of the Hampshire Basin, from the evidence of the Ports- 

 mouth district, are in the main newer than the Middle 

 Oligocene. But evidence obtained lately in Devon seems 

 to show that the folding was of Upper Oligocene or of 

 Lower Miocene date. That is to say, these disturbances 

 date from the same period which saw so much folding, 

 disturbance, and mountain-building throughout Europe, 

 and originated the chief Tertiary basins. The Miocene 

 and Pliocene periods have left no legible traces in this 

 neighbourhood, and all we can say is that during these 



