48 



filled with pumice stoiie, boiled in concentrated sulphuric acid, together 

 with some sulphuric acid. This absorbs any moisture that may be driven 

 off by the heat. (5) This connects again with another U-tube, of which 

 is filled with granulated soda lime, the remaining J in the upper part of 

 the second limb contains chloride of calcium. (6) An aspirator completes 

 the apparatus. 



For the analysis, weigh the absorption tube 5, closed at both ends 

 with small pieces of glass rods in rubber tubing, introduce about 5 to 

 10 grams of the air-dried soil into the decomposing flask, put the appa- 

 ratus together, having previously tested it to see that it does not leak, 

 close the stop-cock of the funnel tube, arid attach the aspirator. The 

 substance can best be weighed in a small piece of glass tubing sealed 

 at one end, into which the soil is placed, and the weight noted ; then, by 

 shaking as much of the substance as possible into the flask, and again 

 reweighiug, the difference between this weight and the former will rep- 

 resent the amount of the soil taken for the determination. 



When the aspirator has produced a partial vacuum, introduce the 

 30 c. c., about, of dilute hydrochloric acid contained in the funnel into 

 the decomposing flask. As soon as all the acid is in close -the stop- 

 cock and apply a gentle heat until the liquid begins to boil. Then re- 

 move the heat, attach the guard tube 1, open the stop-cock, and draw 

 air through the apparatus slowly until the liquid is cool; about 2 liters 

 is sufficient. 



Weigh the absorption tube j the difference between this weight and 

 the first weight of the tube is equivalent to the carbonic acid contained 

 in the quantity of soil taken. 



DETERMINATION OF NITROGEN BY COMBUSTION WITH SODA LIME. 



\ 



To determine the total nitrogen present in the soil proceed as follows : 

 Select a tube of hard glass, 15 to 18 inches long, draw one end of it to 

 a fine point, and to the other end fit tightly a cork, through which is 

 passed a tube bent at right angles, the other end of which passes through 

 a cork closing tightly one arm of a bulbed U-tube. Into the combustion 

 tube first slip a loosely-fitting plug of asbestus, previously ignited, and 

 then some 3 or 4 inches of dry soda-lime. Weigh out 1 gram of the 

 air-dried soil, and mix it in a porcelain mortar with some finely pulver- 

 ized soda-lime, and introduce the mixture into the combustion tube, 

 forcible pressure being carefully avoided. The mixture is followed by 

 a layer of the soda-lime, used to rinse the mortar. Enough granulated 

 soda-lime is then added to fill the tube to 1 or 2 inches of the open end ; 

 place another plug of ignited asbestus at the end, and close with the 

 cork carrying the tube. A free passage is formed for the evolved gases 

 by a few gentle taps, and it is then ready to be placed in the combus- 

 tion furnace, after first ascertaining that the apparatus is air-tight. 



Introduce from a burette into the U-tube 10 c c. of fifth normal oxalic 

 acid, equal to 0.028 gram of nitrogen. This is prepared by dissolving 12.6 



