soil. PHYSICS, CHEMISTRY AND MICROBIOLOGY 



1587 



they may be more or less spherical as in A . infrada and A . venata or flat- 

 tened as in A. moloneyi. The envelope of the spherical forms usually 

 consists of three thicknesses of silk : the outer "layer more or less papery 

 in texture ; the middle layer, composed of loosety spun silk arranged in a 

 number of superimposed sheets ; the innermost layer, hard and parch- 

 ment-like. The envelope of the flattened colonies is made up of a sin- 

 gle layer of closely interlaced silk. The silk of both nests and cocoons is 

 naturally brown in colour, but in the absence of light the worms pro- 

 duce a white silk, and for this reason the natives in parts of Nigeria some- 

 times enclose them in calabashes. 



Anaphe silk cannot be reeled as is done in the case of silk from Bom- 

 hyx mori, and it is therefore carded and spun as " waste " silk ; but apart 

 from this it more closely resembles B. mori silk than does any other kind. 

 It takes dyes well and has been found useful for the manufacture of velvet, 

 sewing silks and other materials. The degummed silk has been valued 

 at about is per, lb but owing to the large amount of labour required to 

 free the silk from extraneous matter, the crude material if shipped to 

 the United Kingdom would only realize about id or 2d per lb. If how- 

 ever, the silk were cleaned locally by the natives, the clean product might 

 be worth 6^ per lb. in London. 



It has been shown experimentally in Uganda that the worms can be 

 successfull}^ domesticated and there seems to be no reason why a iiew 

 industry should not be established in Africa. 



CROPS AND CUIvTIVATION. 



1 163 - Cause and Nature of Soil Acidity witli special Regard to Colloids and Adsorption. 



— Truog E., in Journal fiir Physikalische Chemie, Vol. XX, pp. 457-484 191 6; abstract in 

 Journal of the Society of Chemical Industry, Vol. XXXV No. 15, pp. 855 856. London, Au- 

 gust 15, 1916. 



The production of acidity or alkalinity when certain neutral solutions 

 come into contact with certain solids is probably due to chemical action 

 and not to selective adsorption of ions. Cameron's contention that the 

 acid reaction towards litmus of washed absorbent cotton (and inferent- 

 tially of certain soils) is due to the adsorption of cations, is untenable, 

 since such cotton has been found to contain an insoluble fatty acid (per- 

 haps margaric acid), which would not be completely removed by the 

 washings with alkali and acid. When cotton is brought into a neutral salt 

 solution, the salt reacts with the fatty acid, some cations are removed 

 and an equivalent amount of soluble acid liberated. Similarly, the re- 

 puted selective adsorption of ions by charcoal is accounted for by che- 

 mical actions between impurities contained in it and the dissolved salt. 



Assuming selective adsorption, the vastly greater adsorptive power 

 of soils would still need explanation. Arguments are also adduced to 

 prove that soil acidity is not the result of selective ion-adsorption, by 

 colloids or by finely divided solids ; and it is shown experimentally that 



SOIL PHYSICS, 



CHEMISTRY 



AND 



MICROBIOLOGY 



