CALCAREOUS MANURES— PRACTICE. 153 



or defect ; if the filtering paper operates well, throw out the water, and 

 pour into it the whole mixture. The fluid will slowly pass through into a 

 glass under the funnel, leaving on the filter all the solid parts, on which 

 water must be poured once or twice, so as to wash out, and convey to the 

 solution, every remaining particle of the dissolved lime. 



4th. The solid matter left, after being thus washed, must be talcen out of 

 the funnel on the paper, and carefully and thoroughly dried — then scraped 

 off the paper and weighed. The weight, say 27 grains, being deducted 

 from the original quantity, 50, would make the part dissolved (,50 — 27= 

 23) 46 per cent, of the whole. And such may be taken as very neaiiy 

 the proportion of calcareous earth (or carbonate of lime) in the earth 

 examined. But as there will necessarily be some loss in the process, and 

 every grain taken from the solid parts appears in the result as a grain 

 added to the carbonate of lime, it will be right in such partial trials to 

 allow about two per cent, for loss, which allowance will reduce the forego- 

 ing statement to 44 per cent, of carbonate of lime. 



6th. But it is not necessary to rely altogether on the estimate obtained 

 by subtraction, as it may be proved by comparison with the next step of 

 the process. Into the solution (and the washings) which passed through 

 the filter, pour gradually a solution of carbonate of potash. The first 

 effect of the alkaline substance, thus added, will be to take up any 

 excess of muriatic acid in the fluid — and next, to precipitate the lime (now 

 converted again to carbonate of lime,) in a thick curd-like form. When 

 the precipitation is ended, and the fluid retains a strong taste of the carbo- 

 nate of potash, (showing it to remain in excess,) the whole must be poured 

 on another filtering paper, and (as before,) the solid matter left thereon re- 

 peatedly washed by pouring on water, then dried, scraped off', and weighed. 

 This will be the actual proportion of the calcareous part of the sample, ex- 

 cept, perhaps, a loss of one or two grains in the hundred. The loss, there- 

 fore, in this part of the process apparently lessens, as the loss in the earlier 

 part increases the statement of the strength of the manure. The whole 

 may be supposed to stand then : 



27 grains of sand and clay ^ 



21 of carbonate of lime ^=50. 



2 of loss ) 



If the loss be divided between the carbonate of lime and the other worth- 

 less parts of the manure, it will make the proportion 28 and 22, which will 

 be probably near the actual proportions. 



The foregoing method is not the most exact, but is sufficiently so for 

 practical use. All the errors to which it is liable will not much affect the 

 reported result— unless magnesia is present, and that is not often in ma- 

 nures of this nature. Magnesia is never found (I believe) in the deposites 

 of fossil shells— nor have I known of its presence in any of the earthy ma- 

 nures, except lime-stone, and the magnesian marl discovered in Hanover. 

 If any considerable proportion of carbonate of magnesia should ever be 

 present in marl tried by the foregoing method, it may be suspected by 

 the effervescence being very slow compared to that of carbonate of lime 

 alone ; and the proportions of these two earths may be ascertained as fol- 

 lows. The magnesia as well as the lime would be dissolved by the mu- 

 riatic acid, (applied as above directed,) but the magnesia would not be pre- 

 cipitated with the carbonate of lime, but would remain dissolved in the 

 alkaline solution, last separated by filtering. If this liquor is poured into a 

 Florence flask and boiled for a quarter of an hour, the carbonate of mag- 

 nesia will fall to the bottom, and may then be separated by filtering and 

 washing, and its quantity ascertained by being dried and weighed. This 



