1 68 Son, Analysis [285 



straight glass tube with a piece- of india-rubber tubing and a 

 soda lime tube attached in the same manner as shown in 

 fig. 22. 



Weigh out from 2 to 8 grams of the soil, according to its 

 nature, into the flask, and add first 20 c.c. of water, then 30 c.c. 

 of strong sulphuric acid. Now connect the flask directly with the 

 aspirator, so that the C0 2 formed in the flask by decomposition 

 of the carbonates may be drawn off. Whilst this is proceeding, 

 weigh the U tube (f, fig. 22), and place all the tubes together. 

 Next connect up the apparatus as shown in the figure. Take 

 the cork out of the flask, and introduce 8 grams of coarsely 

 powdered pure potassic dichromate. Close the flask again, and 

 heat gently as long as gas is evolved; then heat nearly to 

 boiling for some time. Finally, aspirate air through the appa- 

 ratus for about ten minutes. Detach the weighed U tube, 

 allow it to cool, and weigh again. The increase of weight is 

 due to the C0 2 formed from the oxidation of the humus. If 

 this amount of C0 2 be multiplied by '471, the weight of humus 

 is obtained. 



ANALYSIS OF THE PORTION INSOLUBLE IN 

 HYDROCHLORIC ACID 



The actual analysis of this portion of the soil is exactly 

 similar to the analysis of the soluble portion, the only difficulty 

 being to get it into solution. This is accomplished by one of 

 three methods. 



285. The Sulphuric Acid Method.— Weigh out roughly 

 2 grams of the insoluble portion of the soil in a weighed plati- 

 num dish. Ignite over an Argand, allow to cool in a desic- 

 cator, and weigh accurately. Add 10 c.c. of strong sulphuric 

 acid, and heat on an Argand very cautiously. This operation 

 must be carried on in a draught cupboard, as the heating has 



