312 ANALYZING OF MAftL. 



thereon repeatedly washed by pouring on water, then dried, scraped 

 off, and weighed. This will be the actual proportion of the calca- 

 reous part of the sample, except, perhaps, a loss of one or two 

 grains in the hundred. The loss, therefore, in this part of the pro- 

 cess apparently lessens, as the loss in the earlier part increases the 

 statement of the strength of the manure. The whole may be sup- 

 posed to stand then : 



27 grains of sand and clay 

 21 " of carbonate of lime 

 2 " of loss _ 



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

 worthless 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 manures of this nature. I have never found carbo- 

 nate of magnesia in any of the deposits of fossil shells in Virginia, 

 though it was in many cases sought for.* If, however, a>ny consi- 

 derable 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 ascer- 

 tained as follows : The magnesia as well as the lime would be dis- 

 solved by the muriatic acid (applied as above directed), but the 

 magnesia would not be precipitated 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 magnesia will fall to the 

 bottom, and may then be separated by filtering and washing, and 

 its quantity ascertained by being dried and weighed. (Davy.) 

 This part of the process may be added to the foregoing, but it will 

 very rarely be required. 



If desired, the proportions of sand and clay (besides the calcare- 

 ous parts of each) may be ascertained with enough truth for prac- 

 tical purposes, by stirring well the remaining solid matter in a 



* Carbonate of magnesia is known to me only in one case. This is of a 

 peculiar compound of carbonates^ lime and magnesia with other common 

 earths, found on Bear Creek IsnBin Hanover county, above the falls of 

 Pamunkcy. I have seen it only in a specimen sent to me fifteen years ago, 

 and of which analyses were made both by Prof. W. B. Rogers and myself, 

 in different modes, with like results. I presume this earth must have been 

 found in very small quantity, as I have never heard of its being used as 

 manure, nor indeed anything else about it. 



Prof. C. U. Shepherd reports magnesia found by him in some of the rich 

 eocene marls of South Carolina. I had before sought for it in vain, in many 

 other specimens of the same general kind of marl. 



