The Siemens large and small pulverizers >*iich are provided with claws can destroy 

 the densest plant covers in two working operations (see Fig. 50 and 51), The large 

 pulverizer, vihose wheel rims can be provided with "marsh extensions" for soft soiled 

 ponds, and vriiich has a working breadth of 160 centimeters (6^ inches), receives first 

 consideration for large industries. The total costs of the pulverization work are said 

 to be about 60.00 marks per hectare (or $5.75 per acre). The Siemens small pulverizer, 

 which is also suited for small industries, has a working breadth of 70 centimeters 

 (28 inches) and a working depth up to 30 centimeters (12 inches) according to selection 

 and the soil character. The surface jdeld amounts to from 50 to 60 ares (1.23 to 1.A8 

 acres) per hoiir, I shall finally remark in general that cultivation of the soil and 

 plowing up to a depth of 15-25 centimeters (6 to 10 inches) is mostly correct. On the 

 drained pond' bottom, any projecting columnar clumps of above-water plants (see Fig. 20) 

 may be lifted out with a Sacks No. Li one-shared plow which is drawn by horses. For 

 sawing them at the ground, a Uaurer or clump saw, wnich is operated by four men, is 

 used. It consists of a horizontal lying saw blade with a tension frame about 150 centi- 

 meters (5 feet) high, similar to a joiner's buck-saw. Two people guide the frame, two 

 pull bade and forth on ropes attached to the base of the frame. In large industries 

 motor saws, very suitable for this purpose, may be used. 



F. Liming . 



Liming- La a. means of pond care, which has to serve particularly many different 

 purposes. On the one side it protects the health of fishes in various ways, and on the 

 other side, it increases production by producing favorable production biological con- 

 ditions, which react to iii crease the yield. 



These various actions are obtained in t he following ways 



(1) A suitably applied liming kills, by caustic action or by toxic and 

 caustic action, the bottom dwelling, freely swimming stages, resistant 

 stages, eggs, and intermediate stages of parasites living in intermediate 

 hosts (snails), parasite carrying fishes, and also for a brief time algae 

 and water plants without deep roots. In a short time the lime is chemical- 

 ly transformed and becomes harmless to fishes, 



(2) The low pH value of acid waters will be raised, through liming to the 

 normal value of slightly alkaline waters. Dissolved and noxious iron 

 will eventually become neutralized and precipitated. The slightly alka- 

 line reaction of pond water (pH value 7 to 8) is: 



a. Most favorable to the health of fish. 



b. Ib absolutely necessary for favorable conditions of the metabolic 

 cycle and of all other measures for an intensified culture. 



(3) Lining will raise the acid combining value, A.C.V. This in turn — ^s long 

 as the A.C. value is greater than 0.5 to 1 — will: 



a. Prevent extreme changes in the pH value, either upward or downward. 



b. TTill create a carbonic acid reserve making a carbonic acid minimum 

 impossible; (as accepted by Zuntz 1913 and later by Czensny). 



c. Will preserve sufficient Ca as necessary nutrients for plants and 

 aquatics; and for building animal shells, carapaces and other 

 substances. 



d. By the presence of enough calcium, any soluble magnesium, sodium 

 and potassium compounds are "detoxicated" . Solutions of any one 

 of these salts alone cause distinctly toxic reactions, according 

 to Schumann, 



162 



