41 



ate which effervesces violently when the acid is added, thus causing a 

 loss of some of the substance. 



It is a good plan to add to the weighed precipitate more sulphuric acid 

 and proceed as before, until you get a constant weight. The weight of 

 the calcium sulphate found multiplied by 0.41158 will give the weight 

 of the calcium oxide, lime, and this divided by the weight of the soil 

 taken for analysis and multiplied by 100 will give the percentage of 

 lime present in the soil. (Fres., 154, 6, a : and 103, &, .) 



DETERMINATION OF THE MAGNESIA. 



Make the combined filtrates from the calcium oxalate alkaline with 

 ammonia, if not already so ; add 30 c. c. of a solution of hydro di-sodic 

 phosphate. Agitate the contents of the beaker with a glass rod, tak- 

 ing care not to rub the sides, as it will cause crystals of ammonium mag- 

 nesium phosphate to adhere to the sides very difficult to remove. Al- 

 low the solution to stand for twelve hours in a cool place. Filter off 

 the clear fluid through a weighed Gooch crucible;* transfer the pre- 

 cipitate and wash with dilute ammonia, prepared by mixing one part 

 of the strong ammonia with three parts of distilled water. In case any 

 particles of the precipitate adhere to the sides of the beaker, rub them 

 off as much as possible with a rubber- covered glass rod, and wash them 

 onto the main precipitate in the crucible. Whatever cannot be so de- 

 tached are moistened with a few drops of acetic acid, transferred to a 

 smaller beaker, made alkaline with ammonia, and set aside for six hours 

 for the precipitate to settle, and it is then added to the main precipi- 

 tate. 



The precipitate is washed well with the ammonical water, the cruci- 

 ble and contents ignited gently at first and afterwards over a blast lamp. 

 By the action of the heat the ammonium magnesium phosphate is trans- 

 formed into magnesium pyrophosphate, Mg 2 P 2 O 7 . Cool the crucible 

 and contents in a desiccator and weigh. The increase in the weight of 

 the crucible represents the weight of the magnesium pyrophosphate ; this 

 multiplied by 0.36024 will give the weight of magnesia, MgO, present, 

 from whence the percentage is readily calculated. (Fres.. 154, 6, a. 

 104, 2.) 



SEPARATION OF THE ALKALIES FROM THE OTHER BASES PRESENT. 



In 200 c. c. of the solution B, equal to 4 grams of the air dried soil, 

 proceed to determine the potash and soda, in duplicate, as follows : 

 Evaporate each 100 c. c. of the solution nearly to dryuess in order to 

 drive off as much free acid as possible; then dilute with about 75 c. c- 

 of warm water and heat on the steam bath for half an hour. Add am- 

 monia till the solution is nearly neutralized and then 25 c. c. of a sat- 

 urated solution of barium hvdrate, so that thefluid*is strongly alkaline 

 * Proc. Amer. Acad. Arts aud Sciences, 1878, p. :i4vJ 



