86 ON DRAINING. 



nearer the outfall end of a line of drain ; and for the very 

 obvious reason, that the flow of water there is greatly less 

 both in quantity and velocity, and consequently of less 

 force, than it is as it approaches the end of its course. This 

 specimen was analyzed by Mr. Richard Phillips, of the 

 Geological Museum, Craig"'s Court, London. Mr. Phillips 

 at once told me it was peroxide of iron, but I wished it to 

 be analyzed that I mig'ht know whether, and to what extent, 

 the iron was pure or incorporated with other matter. The 

 following- is Mr. Phillips's report of its nature and of the 

 manner of its production : — 



" 3Iuseum of Geology, 13th Dec. 1845. 

 " I have submitted the deposit occurring in the drainmg-pipes to 

 analysis, and I find it to consist of, after drying, — 



Silica and alumina, witli a trace of lime .... 49'2 



Peroxide of iron 27"8 



Organic matter 23'0 



100-0 



" The large amount of peroxide of iron showTi in the above 'analysis, 

 appears to me to be in consequence of the iron existing originally in a 

 lower state of oxidation, in which state it has been dissolved by carbonic 

 acid, and formed by the decay of organic matter in the soil, and then 

 carried away by the drainage water ; when, by subsequent exposure to 

 atmospheric air, it has been converted into insoluble peroxide. The other 

 ingredients in the deposit would appear to have been carried down me- 

 chanically, in consequence of their existing in a very minute state of 

 division." 



It thus appeared from the analysis that only 27*8 per cent. 

 of the deposit consisted of iron, and that the remainder, 

 nearly three-fourths of the whole, consisted of foreig-n matter. 

 This analysis powerfully fortified my hopes that the drains 

 I was making- mig-ht remain permanently open, if their me- 

 chanical structure were such as to admit water only, and no 

 other earthy matters than such as mig-ht be chemically dis- 

 solved, in which case it was apparent that I should reduce 

 the enemy to be contended with by nearly three-fourths of 

 his streng-th, and direct ag-ainst him, for expulsion, a more 

 concentrated stream of water, by reason of the smaller di- 

 mensions of the conduit. Between November last and the 

 present time, some miles of drains have beeTi executed in the 

 soils referred to, abounding- with bog- iron-ore, locally called 

 " pox-stone," the same as I have met with in North Devon 

 under the name of " black-ram," and in Somerset under the 

 title of "iron-mould." In other parts it is called by its 

 proper name. It occurs in masses, both larg-e and small. 



