APPENDIX III 799 



points distributed over the entire sampling section. All necessary precau- 

 tions shall be observed in taking samples, and in observing the end-point 

 of the reaction during titration. 



In short tests, care shall be taken to preserve a uniform rate of intro- 

 duction of the dosing solution. Preliminary observations shall be made to 

 determine the time required after the dosing is started for uniform conditions 

 to become established at the sampling station; and in the actual tests the 

 dosing shall be continued for double this time before sampling is begun. 

 Uniformity of dilution of samples both with respect to location in the section 

 and the time of taking shall be considered essential for an acceptable test. 



POWER TESTS OF TURBINE SUPPLEMENTED BY EFFICIENCY TESTS OF A MODEL 



10. When the conditions of an installation are such as to involve serious 

 difficulty or expense in the application of any of the above methods of water 

 measurement, the tests of the installed turbine may be made when accept- 

 able to both parties without measuring the quantity of water, a homologous 

 model of the turbine being constructed and tested at the expense of the 

 purchaser, and the power delivered by the installed turbine compared with 

 that computed from the model tests. 



This method must not be confused with the practice, which has some- 

 times been followed, of comparing a turbine with a model having a homol- 

 ogous runner, but dissimilar with respect to setting, draft tube or other parls. 

 The runner, guide vanes, draft tube, casing, or other adjacent water passages 

 should be geometrically similar in the turbine and model; and when so 

 constructed, the power stepped up from the model tests for the hydraulic 

 equivalent of the speed gives a reliable basis of comparison with the power 

 actually obtained from the installed unit. 



The power of the model when operating at the hydraulic equivalent 

 of the speed of the large unit in the tests of the latter, at the same propor- 

 tional gate opening, is to be multiplied by the ratio of the area of the discharge 

 orifices of the large turbine runner to that of the model, and by the three- 

 halves power of the ratio of the head existing in the tests of the large unit 

 to the head in the model tests. When the power so computed agrees exactly 

 with that obtained from the installed unit, the efficiency of the large unit 

 shall be considered to be identical with that of the model; and when the 

 power of the large unit exceeds that thus computed from the model, the 

 efficiency of the large unit shall be considered to be in excess of that of the 

 model. In measuring the gate opening the actual opening of the gates shall 

 be determined, and care shall be taken to avoid errors due to the effect of 

 the pressure on the vanes. 



APPENDIX 



11. Special Methods of Water Measurement. The following methods 

 of water measurements may sometimes be applied; these are, however, 

 subject to limitations, and are available only under special conditions. 

 They have not as a rule been in sufficiently general use in turbine testing 

 to permit full reliance to be placed on them until opportunities are afforded 

 for checking them against the methods already given. 



(a) By the Bulk or Volumetric Method. Water measurement by weight 



