In all regions of low calcium water, the fishbreeder must know hov; to determine the 

 pH rate and to constantly keep check of it. Of the many methods in use for such purposes, 

 we recommend — as especially simple and giving sufficiently correct figures — the method by 

 means of Merk ' s Universal Indicator . 



One needs for this: 



(1) tork's Universal Indicator (to be had at P. Altmann). Vie recommend 

 the phenophthalein indicator, according to Gzensny which gives better 

 colorings at pH rates of from 7.5 to 9.5. 



(2) Glass tubes of 12 millimeter diameter or white porcelain cups (egg cups). 



Add 4 drops of universal indicator to 5 cc of the test water. Like litmus, the in- 

 dicator reacts with different colors, with this difference though, that its color scale is 

 more finely divided than the litmus scale. V.ith the aid of the scale as given here in 

 table 6, (first published by Czensny in 1929) one can now determine the pH rate with an 

 error of ^» 0.3 to 0.5, i.e. sufficient for all practical purposes. 



Table 6. 



Color tfcale of Uerk's Universal Indicator with 

 added phenophthalein by pH rates of from It.I^ to 10, 



A still more exact pH test — up to differences of Hh 0.1 in pH — is possible with 

 Czensny's graduated colorimeter (also to be had at Altmann's). After proceeding as before, 

 the colors are then compared with different glass tubes, graded as to colors and v^ich 

 color solutions are sealed into these tubes. The apparatus has been especially designed 

 for fishbreede]?s use and is very handy and reliable. 



To determine the pH rate with still greater exactness, i.e. differences of from + 

 0.1 to 0.2, is in practice as well as for all pond-cultural purposes mostly nonsensical, 

 since extreuely slight variations will naturally occur and dc not mean anything for 

 practical purposes. Complicated apparatuses, so designed, are therefore impracticable 

 for the fishbreeder. 



The Hydrochloric Acid Combining Power 

 (calcium (CaO) and carbonic acid content). 



The functions of carbonic acid and of oxygen in ponds are closely inter- related, 

 ".'.■here green plants liberate oxygen, carbonic acid is consumed; where consumers and re- 

 ducers use oxygen, carbonic acid is produced. 



53 



