742 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, vii.-xi., 



xi. The Action of Naphthalene in Soil. 



The action of certain chemicals, used as fungicides, in increas- 

 ing the yield of crop, has been frequently noted. Of these, per- 

 haps, the most conspicuous example is the effect of spraying 

 potatoes with Bordeaux mixture. As a rule, the treatment shows 

 that the mixture has a decided manurial effect. We do not 

 know, however, whether it is the lime or the copper that pro- 

 duces the result, and, in a series of tests upon the growth of 

 bacteria in soils, that I made with copper sulphate, lime, a 

 mixture of these and with superphosphate, the results were 

 negative; that is to say, the control-test showed a greater number 

 of bacteria, from time to time, than any of the others. 



Meanwhile, Mr. Hugh Dixson called my attention to the pro- 

 posed use of sulphur and naphthalene in horticultural practice. 

 Both are said to augment the crop in unsterilised soils, and I 

 decided to test them, with regard to any action they might have 

 upon the increase of bacteria. The sulphur was used as precipi- 

 tated sulphur, and the naphthalene as "vapo-naphtha," generally 

 used, in conjunction with lime, for destroying injurious insects. 

 In a previous paper, I showed that sodium thiosulphate increased 

 the growth of bacteria in soil-extracts, and, as the same might 

 occur in soils, it was used with other salts in an experiment. The 

 test was made upon soils contained in bottles closed with a cork 

 furnished with a glass tube drawn out to an open capillary point, 

 and were incubated at 22°. 



Experiment i. 



