24 Estimations occurring in Agricultural Analysis [30-33 



test is performed should be allowed to stand for about a 

 minute, as it often takes that time before the cloudiness 

 appears. 



30. Burning and Ignition. — The precipitate is dried 

 (paragraph 16) and transferred to a platinum dish, as in the esti- 

 mation of iron. Great care must, however, be taken thoroughly 

 to burn the filter paper on the wire. Any carbonaceous 

 matter dropped into the dish tends to reduce a portion of the 

 BaS0 4 to BaS. This, however, will not take place in a good 

 current of air such as is kept up around the hot wire. Further, 

 it should be mentioned that a shallow dish is preferable to a 

 deep crucible for the ignition. A shallow dish will afford every 

 opportunity for the free circulation of the air; a deep crucible 

 will keep out the air. With these special precautions, the 

 burning of the filter and subsequent ignition over an Argand 

 may be performed as described in paragraphs 20 and 18. 



31. Entry and Calculation. — The results should be 

 entered in the note book as shown in paragraph 26, and the 

 calculation made in much the same way. One molecule of 

 BaS0 4 corresponds to one of S0 3 j or 233 parts by weight of 

 BaS0 4 correspond to 80 parts by weight of S0 3 . 



ESTIMATION OF POTASH 



32. Substance used.— Potassic chloride, KC1. 

 Method employed. — The potassium is precipitated as 



K 2 PtCl G , and weighed as such. 



Weigh out about -3 gram of pure potassic chloride, and 

 wash it off the watch glass into a wide-mouthed beaker 

 2 inches high by 2 inches broad, using as little water as pos- 

 sible. Add sufficient water to dissolve it, then two or three 

 drops of dilute hydrochloric acid. 



33. Precipitation. — Pour into the liquid 6 c.c. of a 10 per 



