242 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Another substance that proved better was cresylic acid, the main 

 constituent of the coal-tar acids on the market during the War. Under 

 the name of " liquid carbolic acid " it used to be sold at 2s. a gallon ; 

 it is now double that price, but it may fall to something approaching 

 the pre-War level. Although it does not volatilize from the soil it is 

 readily oxidized by soil bacteria with formation of products that do 

 no harm to plants. After a short period, therefore, the plants can be 

 set out in the treated soil without fear. 



The method of using cresylic acid is to add one gallon of the acid 

 to 40 gallons of water and apply the mixture to 9 to 18 sq. yards, 

 i.e. 40 to 80 gallons a house, then heavily watering ; in the case of 

 heavy soil the acid is applied in two doses at an interval of 14 days ; 

 the land must previously have been dug over to a depth of 1 spit. 

 Planting can begin at the expiration of one month. Pot experiments 

 show that some degree of watering is necessary, otherwise plants 

 become abnormal ; the foliage becomes variegated and the setting 

 of the trusses hampered. 



One gallon to 9 sq. yards is 79 gallons a house : the cost of 

 79 gallons " liquid carbolic acid " @ 45. the gallon is £15 16s. 

 a house. 49 cwt., costing £105, are needed for an acre. 



The half strength is more usual ; this costs £52 10s. an acre. 



This larger quantity corresponds to about 0.22 per cent, of the 

 soil, or M/50 in the notation explained later. Good results, however, 

 are commonly obtained with the half or M/100 dose, and there is 

 little doubt that the price could come down ; assuming it fell to 25. a 

 gallon, the cost would be only £25 an acre where the half dose proved 

 sufficient. 



On an average of results, carbolic acid is less effective than steam. 

 Thus in blocks of houses under commercial management the following 

 yields of tomatos have been obtained : — 





A. 



B. 



c. 





Steam 



Cresylic acid 



26-0 

 25-4 



32-4* 



22-6 



30-8 



27*3 



tons an acre to end of 

 / September. . 



The cresylic acid fell far behind steam in B, and distinctly behind 

 in C. 



Other chemicals have shown similar inferiority to heat. 



The inferiority of chemicals lies in the fact that they are less certain 

 to act in any given case than heat. Further investigation has empha- 

 sized the important fact that diseases and sicknesses of soil are not one 

 but many, and the only rational way of using chemical agents is to 

 do what medical men did in the case of human beings — make a 

 proper diagnosis of the cause and then seek a specific remedy. 



* Steamed with grids : 30-3 tons an acre when steamed with trays. 



