2+ 



Prevention of Damage by Frost. [april, 



France, and consist of wooden boxes about 10 in. square and 8 in. 

 deep,, containing a resinous compound which produces consider- 

 able smoke when burning. These, however, are far too dear for 

 commercial use, costing nearly i franc each in Bordeaux. Ex- 

 periments were also made with crude naphthalene salts mixed 

 with dry soil, saw-dust, and other materials ; considerable smoke 

 resulted, but little heat, and great difficulty was experienced in 

 keeping the fires alight. 



A cast-iron bucket, as used in California (where the system is 

 known as smudging) was afterwards designed for burning petro- 



leum, but it was found that the receptacle must necessarily be 

 smaller at the top than at the bottom to prevent too rapid com- 

 bustion, and this made it appear impossible to use cast-iron, 

 which we believe would otherwise be preferable to tin. 



Ultimately a tin can, such as appears in the illustration, was 

 designed, the height being 9 in., diameter at base 8J in., diameter 

 at top 61 m. Two rows of round holes, each about f -in. diameter 

 were pierced round the upper part of the can to admit draught. 

 It was necessary to have all the joints grooved, as no soldering 

 would withstand the heat produced. The cost of each can 

 was gd. 



