THE FARMER'S MAGAZINE. 



99 



grass land, and (2) the cost of raising that amount 

 of sewage from its level at the sewer's mouth to 

 the necessary height. 



As regards the quantity of sewage required in 

 irrigation, there are two ways of obtaining an ap- 

 proximate result — either by the amount of water 

 which a dry soil will absorb, or by ascertaining 

 the quantity actually used in the irrigation of cer- 

 tain long-celebrated water-meads. The first mode 

 was that adopted by M. Schubler {Jour. Roy. Ag. 

 Soc. vol. i, p. 182) ; he found that the real quan- 

 tity of water in a saturated cubic-foot of earth was 

 as follows : 



Calcareous sand 

 Silicious sand . 

 Sandy clay 

 Loamy clay . 

 Brick earth-clay 

 Gai'den mould 

 An arable soil . 



31.8 lbs. 



27.3 



38.8 



41.4 



45.4 



48.4 



40.8 



If we calculate the mean amount of water in 

 these seven varieties of saturated soils to be equal 

 to 42 lbs. per cubic-foot of earth, or 378 lbs. per 

 square-yard of soil a foot deep, then 378X4840 

 (tlie number of square-yards in an acre) gives 

 1,829,420 lbs. of water needed to saturate an acre 

 of perfectly dry land to the depth of one foot, or 

 about 816 tons. If we suppose that the saturation 

 of the soil need only extend to a depth of nine 

 inches, then about 543 tons of water would be 

 sufficient; if a depth of only six inches, then 408 

 tons ; and if to only a depth of four inches, then 

 273 tons would suffice. 



The second and more practical method of ascer- 

 taining the most beneficial amount of sewage 

 necessary for irrigating a given quantity of land, 

 is by reference to the quantity employed at Edin- 

 burgh. Here we are fortunately aided by the re- 

 port of two gentlemen well conversant with the 

 management of those valuable meadows. It ap- 

 pears from the report of Dr. J. Stark (" Statement 

 on Sewer Manure," p. 49), that the celebrated 

 Craigentinny Meads are annually irrigated with the 

 city sewage about eighteen times. For instance : a 

 certain plot was watered in its turn, in 1845, May 

 3 and 14, June 3 and 20, August 15 and 31, Oct. 

 8 and 29, Nov. 24, Dec. 31 ; in 1846, Jan. 30, Feb, 

 18, March 5 and 22, April 2 and 13. 



Now, if we calculate that, on an average of months, 

 500 tons of irrigation-water would suffice to saturate 

 the soil (always partially and sometimes thoroughly 

 previously moistened), then it would require 9,400 

 tons of water to give these eighteen irrigations to 

 an acre of land. I deem the quantities I have 

 stated as likely to be an average amount of sewage- 

 fiuid required for the irrigation of an acre of grass- 

 land to be nearly correct. In the report of Mr. 

 George Buchanan, engineer to the Irrigated Meads 

 of Craigentinny, to the Commissioners of Metro- 

 politan Sewers, he states the quantity of water 

 necessary per acre (p. 6) to be equal to a stream of 

 sewer-fluid of 3g: cubic feet per minute for twelve 

 days of ten hours each. Now this I calculate to be 

 equal to 3:i X 60 X 10 x 12 = 23,400 cubic feet, 

 weighing 62| lbs. per cubic foot, or 62^ x 23,400 = 

 1,462,500 lbs., or about 650 tons. It will be re- 



marked, however, that the sewage-fluid in this case 

 had to sustain the soakage, leakage, and evapora- 

 tion during thirteen days of the month of May. 

 This slow irrigation is far from being the most 

 economical mode of applying the sewage — the more 

 rapid and copious application being to be preferred, 

 as affording little time for the soakage into the sub- 

 stratum and the drains. Mr. Buchanan also adds 

 (ibid. p. 7) : " In some parts the soil consists of 

 very stiff' clay, resting on a similar substratum, and 

 other parts of a red sand, and the sand requires 

 nearly twice as much water for saturation as the 

 clay." 



AYe see, then, that the amount stated by Mr. 

 Buchanan of about 700 tons per acre having been 

 used at Edinburgh upon a mead, and subject to 

 many deductions from its saturating power, is not 

 very widely different from the average amount of 

 about 800 tons required, according to Professor 

 Schubler, to saturate the same extent of nearly 

 chemically dry earths. Then, again, by avoiding 

 the soakage and drainage waste of twelve days, 

 and taking the average of moderately retentive 

 soils, a very material saving would undoubtedly be 

 accomplished; and, moreover,by raising the sewage- 

 fluid to the contemplated elevations, it would be 

 available for the use of the irrigator a second time. 

 Upon the whole, therefore, we may safely deem the 

 calculated quantity of about 9,000 tons per acre 

 annually to be a tolerable approximation to the 

 truth. 



The most economical steam-engines for raising 

 large quantities of water are the Cornish engines ; 

 and these will be the engines employed by Com- 

 missioners of Sewers, Irrigation Companies, or 

 where land-owners unite in raising sewage on to 

 their lands. But there are more frequent cases 

 where the landholder would be willing to use for 

 this purpose the ordinary fixed engine, now so 

 commonly to be met with on large estates. 



Let us, then, examine what amount of sewage 

 an ordinary steam-engine can be expected to raise, 

 by the consumption of a given weight of fuel, to 

 different heights; and then let us enquire what 

 the Cornish engines accomplish with the same ex- 

 penditure of firing. First, then, as to the power 

 of the ordinary steam-engine. Now, on this head 

 I was, some time since, favoured with a report from 

 Messrs. Ransomes and Sims, of Ipswich. In this 

 they remark : " Probably we shall not be far from 

 an average if we estimate that the small engines 

 used for agricultural purposes will not raise more 

 than 16,000,000 lbs. one foot high by the con- 

 sumption of 1 cwt. of coals. It must be under- 

 stood that the same weight of coal will lift half the 

 water to twice the height, or one-fourth the water 

 to four times the height, and so on." 



Now, supposing that we have to lift the water 

 from a sewer, or other stream, to the portion of a 

 field which is ten feet above its level, then 1 cwt. of 

 coal will lift to that height one -tenth of 16,000,000 

 lbs., or 1,600,000 lbs. As a gallon of water weighs 

 lOlbs., therefore 160,000 gallons will be lifted; or 

 as 224 gallons weigh a ton, 714 tons of water may 

 be raised 10 feet, with the consumption of only I 

 cwt. of coal : and this is almost exactly equal to an 

 inch in depth oyer seven acres, or m average 



