CENTRAL SCIENTIFIC CO., CHICAGO, U. 8. A. 



455 



No. 12391. 



No. 12394. 



No. 12400. 



12390. SHAKER, Tray Design, for preparing soils for mechanical analysis. Two trays with compart- 



ments for eight bottles each are mounted on a wooden platform attached to a substantial 

 wooden base by four hinged metal supports. The shaking movement is imparted through a 

 worm gear mounted on the same base. Sufficient power will be furnished by a % h. p. 

 "motor. The trays are both made removable for convenience in handling and filling. Com- 

 plete with, sixteen bottles, but without motor $53.50 



12391. BOTTLES, Sterilizer, for use in Nos. 12388 and 12390. Capacity, 8 oz per dozen .90 



SHAKER, Soil Sieve, see No. 12148. 



12394. SHRINKAGE APPARATUS for determining the shrinkage of soils, as described in Hosier and 

 Gustaf son's "Soil Physics Laboratory Manual," and used at the University of Illinois. This 

 is a tray of brass, 3 inches square at the top, with beveled sides to facilitate removal of 

 the soil sample. In use, a piece of cheese cloth is placed on the bottom of the tray, which 

 is then filled with moist soil. The soil block is then removed from the tray and allowed to 



dry. The shrinkage in area may readily be determined by measurement 45.00 



SIEVES for Soil Analysis, see general beading Sieves. 



SOIL CONTENT TESTERS 



12400. CONDUCTIVITY BRIDGE, for determining the soluble salt content of soils; made after designs 



approved by the TJ. S. Bureau of Soils. 



The use of this bridge depends on the fact that the electric current is conducted by the salt 

 in solution and that the conductance of the solution or, conversely, its resistance to the pas- 

 sage of the current, is determined largely by -its concentration. The magnitude of current 

 that will pass is increased by an increase of salt in solution; or the resistance to the pas- 

 sage of the current decreases with the increase of salt. The instrument is of general util- 

 ity in measuring the resistances of solutions of soils. It is designed primarily for use as a 

 field instrument, and finds its greatest use in determinations of "alkali" or harmful excess 

 of soluble salts, frequently present in the soils of arid and semiarid areas. In survey work 

 it gives a convenient method for determining in the field the percentage of alkali in a soil, 

 so that the mapping may be carried on concurrently. It is also useful in determining the salt 

 content of irrigation and seepage waters. 



The instrument, by means of which resistances are measured, is a modified form of slide-wire 

 Wheatstone 'a bridge. In operating the bridge, the cup is filled with the soil saturated with 

 water, and placed in the clips provided for it. The resistance of the cup contents is then 

 read, and from the resistance the amount of soluble salt present determined by reference 

 to the tables given in the Bulletin mentioned above. (See Bulletin 6, U. S. Bureau of Soils.) 



Complete as described $150.00 



Note. Bridges of the above type made by us have proved satisfactory to and met the require- 

 ments of the U. S. Bureau of Soils, Washington, D. C. 



Bridges of this type are used by the Atchison, Topeka & Santa Fe Railway Company for testing 

 the alkali content of their tank water. 



12401. DRT BATTERY, complete, as used in No. 12400 Conductivity Bridge 1.25 



