ESTIMATION OF CARBONATES 



59 



contents are carefully heated to incipient boiling. The 

 flask is then allowed to cool, the stoppers replaced, and 

 the whole apparatus weighed. The loss of weight 

 gives the amount of carbon dioxide in the weight of 

 limestone taken. 



A simplified form of apparatus is shown in Fig. 12. 

 The dilute acid is kept in the small test-tube which 



Fig. 12. — Simplified Schrotter apparatus. 



leans against the walls of the flask. After introducing 

 the material and replacing the stopper, the acid is 

 caused to flow on to the carbonate by tilting the flask. 

 The carbon dioxide escapes by way of the calcium 

 chloride drying tube, and the contents are then heated 

 and aspirated as before. 



This method and apparatus may be used for 

 estimating limestone in very chalky soils, but more 

 accurate methods of estimating small quantities of 

 carbonate present in soil are necessary, and are described 

 under Soil Analysis (75, 76, pp. 94 and 96). 



37. Humus. 



(a) About 5 grams of air-dried soil are carefully 

 weighed out and heated in the steam oven until of 



