206 § 109. ANALYSIS OF SOILS AND EOCKS. 



bonate contained in it, with dilute liydrocldoric acid in a 

 flask, as long as there is any effervescence, wash the resi- 

 due, boil it half an hour with water, and then subject it 

 to the silt analysis (§ 97). 



Or, if it is desired to determine the fineness of division 

 of the calcic carbonate in the marl, the whole may be 

 subjected to the silt analysis without previous treatment 

 with acid, and then the carbonate can be determined in 

 the contents of each funnel. 



If the marl does not fall to a fine powder in water, it 

 must first be sifted, as directed for the preparation of the 

 soil for the silt analysis. 



For practical purposes, the following rough method of 

 estimating the fineness of the marl will often answer. 



After treating 10 grms. of the marl -with hydrochloric 

 acid as long as there is any effervescence, pour a consid- 

 erable quantity of water over the residue, with constant 

 stirring, let the sand and heavier particles settle, and de- 

 cant the turbid liquid holding clay in suspension ; repeat 

 the same operation with the residue several times, until 

 the water is clear after the sand settles to the bottom, 

 collect the latter on the filter, ignite, and weigh as coarse 

 sand. 



The chemical analysis. 



a. Water. — Dry about 10 grms. of the substance at 

 100° C, and determine the loss of weisrht. 



h. Carbonic acid. — Determine this in 2-4 grms., as di- 

 rected in § 60. 



For practical purposes, the following method will usu- 

 ally yield sufiiciently accurate results. 



Weigh out 2-3 grms. of the marl in a flask of about 

 100 c.c. capacity, moisten it with a little water, carefully 

 lower into the flask a small test-tube, ^|j filled with hydro- 

 chloric acid, in such a way that no acid can escape into 

 the flask, and weigh the whole ; then cause the acid to 

 flow out of the test-tube into the flask by inclining the 



