344 AGRICULTURAL ANALYSIS 



bestos, which has been recently ignited, is placed in the end of the 

 tube to be attached to the absorption apparatus, and then 2.5 

 to 3.5 centimeters in depth of the thiosulfate mixture is added. 

 (2) The portion of the substance to be analyzed is intimately 

 mixed with from five to 10 grams of the sugar and sulfur mix- 

 ture. (3) Pour on a piece of glazed paper or in a porcelain 

 mortar a sufficient quantity of thiosulfate mixture to fill a depth of 

 about 25 centimeters of the tube, add the substance to be analyzed, 

 as previously prepared, mix carefully, and pour into the tube, 

 shake down the contents of the tube, clean the paper or mortar 

 with a small quantity of the thiosulfate mixture and pour into 

 the tube, and fill up with soda-lime to within five centimeters of 

 the end of the tube. (4) Place another plug of ignited asbestos 

 at the end of the tube and close with a cork. ( 5 ) Hold the tube 

 in a horizontal position and tap on the table until there is a gas- 

 channel along the top of the tube. (6) Make connection with 

 the U-tube containing the acid, aspirate and see that the apparatus 

 is tight. 



The Combustion. Place the prepared combustion tube in the 

 furnace, letting the ends project, so as not to burn the corks. 

 Commence by heating the soda-lime portion until it is brought 

 to a full red heat. Then turn on slowly jet after jet toward the 

 outer end of the tube, so that the bubbles come off at the rate of 

 two or three a second. When the whole tube is red hot and the 

 evolution of the gas has ceased and the liquid in the U-tube 

 begins to recede toward the furnace, attach the aspirator to the 

 other limb of the U-tube, break off the end of the tube, and draw 

 a current of air through for a few minutes. Detach the U-tube 

 and wash the contents into a beaker or porcelain dish ; add a 

 few drops of the cochineal solution, and titrate. 



306. Observations. In our experience we have found it 

 much more satisfactory to adhere to the earlier directions for 

 preparing the mixture of thiosulfate and alkali. We much pre- 

 fer to make the mixture with soda-lime and without the pre- 

 vious drying of the sodium salt. Ruffle himself says that the 

 sodium thiosulfate should be dry, but not deprived of its water of 



