62 TKENCHING AND SUBSOILING 



B. DOUBLE-EFFECT PLANT. 



Average cost, 600. This capital to be written off in the 

 same number of years, and the same rate of interest. If we 

 assume we plough 80 poles per day, and work 4 days in the 

 year, we arrive at the following : 



Per Annum. 



Writing off and interest at 5 per cent. s. d. 



of 600 in eight years ... ... lOo 



Wear and tear of material at 3 per 



cent, of the capital ... ... 18 



Total ,. 123 



Equal to 3 Is. 6d. per day. 



The daily expenditure is reckoned as follows : 



s. d. 

 One engine-driver ... ... 049 



Three workmen, at 2s. 4d.... ... 070 



Pair bullocks and driver ... ... 4 9 



7cwt. 3qrs. 14lbs. coal (8-8 Ibs. per 

 h.p. hour for a 10 h.p. engine work- 

 ing 10 hours), at 18s. per ton ... 070 

 Oil, cotton waste, putty, &c. ... 020 



Total ... ... 1 5 6 



Plus writing off wear and tear ... 3 1 6 



Daily expenditure ... ... 470 



Which brings the cost of ploughing one acre to 3 9s. 7d. 



We see that for a small grower who does not trench or 

 subsoil more than 50 acres each year the simple-effect plant 

 is more economical than the double effect. In order to 

 derive advantage from the latter we must plough annually 

 at least 72 acres ; for an area of 70 acres, the cost is equal in 

 both systems 2 14s. 5d. per acre. 



It is interesting to ascertain for what area yearly ploughed 

 it is justifiable to use steam-power. 



Assuming that we require two days to plough J acre 

 with a horse-gin, and that the same work can be done by 

 steam in f day, we see that for an area under 30 acres per 

 annum the advantage lies on the side of the horse-gin, and for 

 an area exceeding 30 acres it falls to the side of the steam- 

 power. The cost of one acre in this case comes to 4 Is. 7d. 



