180 TECHNICAL BULLETIN 13 



The cleaning of dairy utensils is not merely "cutting the grease" withi 

 alkali. Milk proteins aresoluble in alkali. But once coagulated or dried, so- 

 lution is very slow even with a strong concentration of alkali. Therefore, 

 something besides alkali nuist be used in cleaning. The cleaning solution must 

 possess deflocculating or emulsifying power so that coalescence of the oily 

 substances into droplets is impossible. This is prevented by the formation of 

 a surface layer of the deflocculant around tiie fat globules. Surface activity is 

 therefore a vital function in the cleaning solution. The detergent must go into 

 true solution, not colloidal or crystalloidal, before it can become oriented and 

 adsorbed upon the surface of the particle. Deflocculation occurs when a cer- 

 tain minimum concentration of "absorbed oriented molecules" of the detergent 

 upon the dirt particle surface has taken place (2). 



Methods of Comparing Washing Powders 



The lirst step in this investigation was logically the cliemical analysis of 

 the various washing powders found on the market. However, the evaluation j 

 of complex and variable materials such as most cleansers are cannot be based 

 upon chemical analysis alone. A properly designed test for performance 

 often affords data of greater practical usefulness. 



No test yet proposed for determining the cleansing efficiency of detergents 

 has received general acceptance, and chemists still depend almost entirelj- 

 upon data of composition for evaluating the respective merits of competitive 

 samples. Such dependence is justified, once the effect of each ingredient has 

 been studied in relation to its use alone and with other ingredients in vary- 

 ing proportions. 



In making laboratory tests, no objections can be raised to tests which close- 

 ly parallel service conditions provided they are not impractical. Such tests 

 may actually prove capable of distinguishing between various samples with 

 sufficient precision for ordinary comparisons. The tests devised for this work, 

 which are described in detail below, may be considered practical in every 

 respect. 



Tests 'based upon the determination of surface tension or interfacial tension 

 appear not entirely satisfactory (3). Such tests show wetting power but this 

 is not necessarily vitally connected with detergent action. The cleaning com- 

 pound must wet the dirt surface, but it must do more than this. It must 

 have the j^owers of emulsification and deflocculation. 



The test of greatest importance is of course the washing power of the 

 powder. Yet this was the hardest test to conduct. Other investigators (4) 

 have found that when using a specific detergent results varied on the average 

 by ten per cent when all conditions insofar as possible were kept constant. 

 With milk in particular the cleaning action is quite varied, depending upon 

 the depth, hardness, et cetera, of the dried or gummed deposit. 



Chemical Analyses of Powders 



In order to ascertain the tj'pes and differences in washing powders on the 

 market, thirty-six brands of powders recommended for dairy use and on sale 

 in Massachusetts were collected. These powders were subjected to chemical 

 analysis to determine the kind and amount of ingredients present. Then the 



(2) Chapin: Ind. and Eng. Chem. 17:1187 (1925). 



(3) Chapin: Ind. and Eng. Chem. 17:461 (1925). 



(4) Luksch: Seifenseeder. Ztg. 40:413. 



