598 Transactions of the American Institute. 



silica, and some organic matter. These were evidently derived fi-om . 

 washings from the surface soil above the shell deposits. When tested 

 under the blow-pipe, and also with phosphate of soda in presence of 

 ammoniacal salts, it showed an entire absence of magnesia. With 

 the blow-pipe, it failed to give any indication of phosphoric acid, 

 but by a careful application of the molybdate of ammonia test, and 

 allowing the liquid to stand for several hours, a very slight precipi- 

 tate, the phosphomolybdate of ammonia, was obtained. This is the 

 most delicate known test for phosphoric acid, and the minuteness of 

 the precipitate obtained shows that a trace, and only a trace, of 

 phosphoric acid exists in the shell-marl of which we are speaking. 

 It may be mentioned here that the blow-pipe test, above alluded to, 

 failed to show the presence of any appreciable portion of alumina. 



The Second Test. 

 After this qualitative treatment the material was subjected to a 

 quantitative test for carbonate of lime, which it was of course evi- 

 dent, constituted its larger portion ; and, inasmuch as the determina- 

 tion of the percentage of carbonate of lime in different substances is 

 at once one of the most common of analytical operations in agricul- 

 tural chemistry, the details of the process may not be without interest 

 to some. A quantity of borax was first vitrified in a suitable vessel, 

 whiclf had been previously weighed. After this the borax was melted 

 in a furnace, and the whole, after cooling, was weighed. The difi'er- 

 ence between the weight thus ascertained and that of the empty vessel, 

 of course, showed the weight of the calcined borax. Meanwhile a 

 quantity of the pulverized shell-marl had been dried over a water- 

 bath until it seemed to lose in weight, and, after being cooled under 

 a desiccator, M'as added to the borax in the dish. The quantity of 

 the marl, in proportion to that of the borax, was about as one to 

 four. After another weighing, to determine the total weight of the 

 two substances, the whole apparatus was placed in a furnace, where 

 it was sufl:ered to remain until the hot mass became perfectly quiet. 

 It was then removed and cooled and weighed again. The loss in 

 weight while in the furnace showed the amount of carbonic acid 

 expelled from the lime by the action of the heat. As carbonic acid 

 always unites with lime in the proportion of twenty-two parts of the 

 acid to twenty-eight parts of lime, a simple calculation shows the 

 weight of the carbonate, which in the present instance amounted to 

 ninety-three and seventy-eight one-hundredths per cent. 



