526 



NA TURE 



[September 20, 1906 



iiiediaie stage when the plant is from 4 inches to 5 inches 

 high. 



Dr. Henry followed with an account of the glucosides 

 containing the hydrogen cyanide, which have been grouped 

 together as cyanogenetic glucosides. They are allied to 

 amygdalin, the active principle in bitter almonds, which is 

 therefore the oldest known representative of the group. 

 The list at present comprises, besides amygdalin, sam- 

 bunigrin, prulaurasin and a glucoside, prepared artificially 

 from amygdalin by Fischer, known as mandelnitrilegluco- 

 side, all of which are resolved by acids into glucose, 

 benzaldehyde and hydrogen cyanide ; further, dhurrin, 

 phaseolunatin, lotusin and gynocardin. 



The plants containing these glucosides also contain 

 enzymes, which resolve them — when the plant is macerated 

 with water — into hydrogen cyanide, glucose and a third 

 constituent. The question was raised as to the rdXe of the 

 hydrogen cyanide, whether it acted protectively or whether 

 it played a part in the production of proteid from nitrates. 

 Dr. Greshoff, of Harlem, dealt with the question from 

 the botanical side, and put forward a list of all the species 

 of plants known to yield hydrogen cyanide, which will be 

 of great value to future workers. 



.A paper on the utilisation of atmospheric nitrogen by 

 plants, read by Mr. Thomas Jamieson, described what 

 the author regarded as special organs in plants adapted for 

 the direct absorption and assimilation of nitrogen from the 

 air. His conclusions were most severely criticised by Prof. 

 Potter from the botanical side, and by Mr. A. D. Hall and 

 others. 



The report on caoutchouc, presented by Mr. S. S. 

 Pickles, contained a general survey of the chemistry of this 

 remarkable product. 



Prof. Karl Harries, of Kiel, in a communication read 

 by Dr. Crossley, dealt with the products obtained by sub- 

 mitting caoutchouc to the action of ozone, and then dis- 

 tilling the ozonide with steam, viz. laevulinic aldehyde, 

 laevulinic acid and hydrogen peroxide. Harries con- 

 cludes that caoutchouc is a polymer of a i : 5-dimethyl- 

 cyclo-octadien. Prof. W. A. Tilden described his observ- 

 ations on the behaviour of isoprene, prepared from oil of 

 turpentine ; when kept it gradually polymerises, being con- 

 verted into a substance having many of the properties of 

 caoutchouc. He also contributed a paper on the con- 

 stituents of Dyera Costtdata. 



Mr. H. H. Robinson followed with a brief account of 

 the chemistry of gums, dwelling especially on gums from 

 India and the colonics which afford acetic acid when ex- 

 posed to the action of moist air. He suggesteS that by 

 partially hydrolysing the inferior Indian gums they might 

 be matie of greater industrial value. In the subsequent 

 discussion, Mr. S. H. Davies stated that constitution had 

 so far been found to have little bearing on the technical 

 value of gums, viscosity being the quality chiefly required. 



In his report, Mr. R. J. Caldwell collected and critically 

 discussed the literature bearing on the hydrolysis of sugars, 

 a subject of considerable interest at the present moment on 

 account of its bearing on the theory of ionic dissociation 

 and the nature of solution. Nearly 150 papers have been 

 published on the subject, so that it is very difficult for a 

 new worker in the field to acquaint himself with the litera- 

 ture. ^ Mr. Caldwell has made a brief abstract of the 

 essential points in each paper, and classified them in 

 historical order under a number of appropriate subheadings. 

 He surns up the evidence as to the nature of the change, 

 and points out the unsatisfactory character of the argu- 

 ment based on the dissociation hypothesis that it is 

 brought about by the hydrogen ions of the acid. He is 

 inclined to believe that the facts are to be explained bv an 

 association hypothesis. 



A large part of the morning of Tuesday, August 7, was 

 devoted to a joint discussion with Section I (physiologv) 

 on the factors which determine minimal diet values. This 

 was opened by Dr. F. G. Hopkins, F.R.S. ; Prof. Dunstan 

 and Prof. Armstrong spoke on the chemical side. It was 

 generally agreed that the subject was of supreme import- 

 ance, and one that should be attacked conjointlv bv 

 chemists and physiologists. Dr. Hopkins dealt chiefly 

 with the standards of minimal diets put forward by 

 .\twater, Voit and Chittenden respectively. These are 

 incorporated in the following table : — 



NO. 1925. VOL. 74] 



Investigator 

 .\twater 

 \-oit 

 Chittenden 



118 

 55 



The methods and results of these workers were con- 

 sidered and criticised in detail. While Atwater's standard 

 was thought to be too high, it was generally agreed that 

 Chittenden's values were too low. Volt's standard was 

 accepted as the most probable. 



Mr. Seebohm Rowntree's well-known experiments carried 

 out in York were referred to, and it was pointed out that 

 in studying actual dietaries of poor families averages were 

 used in compiling statistics, a method which is open to 

 criticism, as the bread-winner^owing to the self-denial of 

 the woman — as a rule, gets far more than his share, so 

 that the diet of the average working man is actually in 

 most cases far richer in protein and has a greater energy 

 value than is imagined. 



Attention was directed by Dr. Hopkins — and this point 

 was particularly emphasised by Prof. Armstrong — that it 

 was not justifiable to consider merely the gross amount of 

 protein, but that the nature of the protein had also to be 

 taken into account. Thus, for example, wheat is probably 

 not the best form of protein, its main constituent, 

 glutaminic acid, being, so far as our present knowledge 

 goes, of relatively little value as a tissue former compared 

 with other amino-acids. Maize protein is perhaps of even 

 lower value, whereas rice and oats, among the cereals, 

 appear to be the especially valuable sources of protein. Prof. 

 .Armstrong particularly referred to the need of making 

 detailed study of foodstuffs, our present method of referring 

 to the nitrogen content generally multiplied by a factor as 

 protein giving no true guide as to the relative value of 

 foods, inasmuch as protein is a highly complex material, 

 made of ever-varying units, the nutritive value of which 

 taken singly varies within wide limits. 



The rest of the morning was devoted to agricultural 

 chemistry, Messrs. A. D. Hall and C. T. Gimingham con- 

 tributing a paper on the action of ammonium salts upon 

 clay and kindred substances, following which Dr. E. J. 

 Russell read a coinmunication by Dr. F. V. Darbishire 

 and himself on oxidation in soils and its relation to pro- 

 ductiveness. These authors have devised an apparatus 

 for measuring the rate of absorption of oxygen ; the power 

 of absorbing this gas possessed by all soils appears to be 

 due mainly, though not entirely, to the activity of micro- 

 organisms. The rate of oxidation does not entirely depend 

 on the amount of organic matter present in the soil ; 

 moisture is essential, and as it increases so also does the 

 rate of oxidation. The rate is also increased by the addi- 

 tion of calcium carbonate or of sugar. For a series of 

 similar soils, of which the cropping power is known, it is 

 found that the most productive has the highest rate of 

 oxidation, and that the others follow in the same order 

 for both properties. The parallelism holds also for soils 

 which have been artificially treated ; it is essential, how- 

 ever, that the soil conditions should be aerobic. The 

 authors suggest that the rate of oxidation affords a 

 measure of the bacterial activity, which is closely connected 

 with productiveness. 



The last paper read was by Mr. W. Popplewell Bloxam, 

 on a new method of determining indigotin. After point- 

 ing out the need of a method of controlling the still very 

 crude processes in vogue for extracting indigo, and the 

 importance of determining the daily yield of indigotin 

 obtained in an ordinary factory from known weights of 

 green plant, the existing methods of analysis were dis- 

 cussed and the uncertainty of the results they afford 

 alluded to. In the author's method, the indigotin is 

 sulphonated by treatment with fuming sulphuric acid 

 (containing 20 per cent, sulphur trioxide) ; the solution is 

 then diluted, and the potassium salt of indigotin tetra- 

 sulphonate precipitated by means of potassium acetate. 

 Finally, the amount of indigotin in the salt is estimated 

 by titration with potassium permanganate or titanium 

 chloride. The author concludes that the present process of 

 manufacture is a wasteful one, the highest efficiency 

 attained not reaching 50 per cent., whilst on the average 

 only 25 per cent, of the indigotin in the leaves is extracted. 



