0)1 Irrigation. 4G9 



of soil find an extensive layer of rock, it dissolves more mineral 

 matter ; and that is doubtless another reason why waters that are warm 

 in winter are more beneficial for irrigating purposes than those the 

 temperature of which is influenced by that of the air. 



I do not think hardness in water is prejudicial to irrigation. I can, 

 indeed, give practical evidence to the contrary. Some of the irrigated 

 meadovv's in the ncighbom-hood of Cirencester, and in other parts of 

 Gloucestershire, are irrigated with very hard water, and the effect pro- 

 duced on them is marvellous. I can conceive that on some land the 

 lime that is conveyed to it in the shape of water is of no advantage ; 

 but I cannot conceive how lime in water can have an injurious effect. 

 Let me give you an illustration showing how apt men are, who perhaps 

 take a little too much credit for their practical sense, to theorise, 

 notwithstanding their strong protestations to the contrary. Practical 

 writers on the subject of irrigation have remarked that soft waters are 

 good, because their softness is due to a soapy constituent — potash or 

 some kind of alkali. Now chemical examination shows that soft 

 rrater generally contains no traces of alkali. It is the hard waters 

 v/hich usually contain the most potash and soda, for the simple reason 

 that, as they traverse soil or rock, potash and soda must be dissolved 

 at the same time as the mineral substances, which they take up. As a 

 matter of fact I may mention that it is the hard waters that contain 

 alkalis, not those which feel greasy and soft ; these last are soft simply 

 because of the absence of mineral matters, such as lime, oxide of iron, 

 and magnesia. 



The best spring-waters for irrigation are those which contain the 

 largest quantity of fertilising matters, especially mineral matters, in 

 solution, and which contain also the most heat, and are thus in the 

 best condition for yielding to the soil over which they pass both food 

 and warmth. 



In conclusion, I would allude briefly to the waters v/hich either are 

 altogether unfit, or else require special treatment to fit them for irriga- 

 tion. Such are the waters v/hich rise from peaty or boggy ground ; 

 these positively do harm. I have foimd it stated that it is the tannin 

 dissolved in the water that does mischief; but this is evidently a 

 mistake. Tannin is a substance which is very rapidly affected and 

 destroyed by atmospheric influences ; so that in tanning care 

 must be taken to bring the materials used as soon as possible in 

 contact with liquids containing tannin. We use solutions containing 

 tannin as a test to ascertain the presence of oxygen. Tannin, then, is 

 evidently not the injurious thing which it is sometimes supposed to be, 

 v/hen it is present in peaty v/atcrs. Nor are the organic acids which 

 are known to the chemist under the name of ulmic or humic acids as 

 injurious in water as some have considered them. In peaty waters the 

 quantity of these acids is but small ; and it is very doubtful whether 

 they produce any injurious effect upon vegetation. But there is very 

 frequently present in peaty water sulphate of iron, or green vitriol; 

 and this is the constituent that does all the mischief. Waters con- 

 taining this ingredient are recognised by the ochrous deposit they 

 produce in their channel-bed. Sometimes waters which flow through 



