402 SECTIONAL TRANSACTIONS.— B. 



micro-methods the research would have entailed the growth and drying 

 of so much plant material as to render it quite unfeasible ; nitrate, potash, 

 phosphate, calcium, magnesium and approximate silica were determined 

 in about 200 samples, which on the macro scale would have involved 

 enormously increased labour. 



Another application of micro-methods actively in progress is in the 

 analysis of dust, especially in connection with work on silicosis and allied 

 diseases caused by the inhalation of dangerous dusts. Micro-methods 

 enable a quantitative gravimetric analysis to be carried out on a total of 

 about 50 mgm. of material, the analyses including silica, iron, alumina, 

 calcium, magnesium, sodium, potassium and loss on ignition. 



The methods are also capable of application in the cement and glass 

 industries, the paper industry and many other industries, and preliminary 

 work on some of these applications is at present in progress. This shows 

 that a trained analyst can learn micro-methods extremely rapidly and in 

 the first week of work attain, for example, figures for silica in glass with 

 errors of less than ± o- 1 per cent, difference from the calculated value. 



A brief description is given of methods for the determination of silica, iron, 

 sulphate, phosphate and nitrate which are found to give good results on the 

 micro-scale. 



Dr. H. Jackson. — Technique of hydrogenation [Demonstration) (11.55). 



A short survey is given of various types of apparatus which have been 

 devised during the past few years for the accurate micro-estimation of the 

 degree of unsaturation of organic compounds, together with a more detailed 

 account and demonstration of the technique used in a particular form of 

 apparatus. This is followed by a description and demonstration of the 

 application of the technique to the construction of an all glass, quantitative 

 system functioning at atmospheric pressure, which is designed to cover all 

 ordinary laboratory requirements. 



Dr. K. K. Nygaard and Dr. Th. Guthe. — Application of the photo- 

 electric principle to the determination of ascorbic acid (12.5). 



By the use of an original, previously described apparatus termed the 

 Photelgraph, the authors have succeeded in automatically recording, by 

 the photo-electric principle, various processes in which a relative change 

 in trans-illumination of the specimen occurs during the process. (Coagula- 

 tion of blood ; The Wassermann reaction.) 



This principle has been applied to a study of the well-known specific 

 reduction of a solution of methylene-blue under the influence of artificial 

 light in the presence of ascorbic acid. Under standardised conditions this 

 process is quantitative as concerns each of the three main factors participat- 

 ing in this photo-chemical process. 



The present method records automatically and graphically on photo- 

 sensitive paper the degree of reduction taking place. 



With constant, known values of the artificial light, exposing methylene- 

 blue solution of known, constant concentration, the geometric appearance 

 of the tracing obtained indicates indirectly the quantity of the third and 

 variable factor, the ascorbic acid. This quantity expressed in micro- 

 grams per cm* of solution is obtained by comparison of the tracing with 

 that of a solution containing a known concentration of ascorbic acid. 



By this method it has been possible to determine quantities less than 

 0-05 microgram of ascorbic acid per 100 cm' of solution. 



General Discussion (12.20). 



