25 



It is, of course, impossible to give here a summary of the mass of 

 information, chiefly of a technical character, witli regard to the 

 detergent action of various soaps and soap substitutes and their effect 

 upon various textiles, but the chief theoretical results will be referred 

 to. 



Krafft has quite rightly insisted that the soaps must be in solution 

 in order that such solutions should exhibit appreciable detergent 

 action. Thus in cold water sodium palmitate and stearate are nearly 

 insoluble, whilst the soluble oleate is an ideal detergent, and even 

 the only moderately soluble laurate and rosinate wash fairly well. 

 Hot water is necessary for the use of tallow soaps, which consist 

 largely of palmitate and stearate ; as Jackson (Cantor Lecturer) has 

 pointed out, potassium soaps are more soluble in the cold than sodium 

 soaps. We would add here the deduction from our measurements of 

 the amount of ionic micelle present in various pure soap solutions, that 

 the washing power which the oleates exhibit par excellence is connected 

 with the fact that their colloidal nature persists well into dilute 

 solutions ; whilst the laurate in dilute solutions and more especially 

 at higher temperatures is largely broken down to simple electrolyte. 

 For this reason, stearate is suitable for washing at the boiling point, 

 since at this temperature it is soluble and it contains much more 

 colloid than the lower soaps. Such considerations are of importance, 

 for example in the choice of a suitable soap for the washing of -woollen 

 goods in the cold. 



EarUer theoretical writers, such as Chevreul, Berzelius, Persoz, 

 von Bussy, Waren-Delarne, Kjiapp, Stiepel and Moride emphasized 

 the emulsifjdng powers of soap solutions and of soap foam towards 

 fats and fatty materials. The capacity of soap solutions to wet 

 oily matter was also emphasized whilst the unknown amount of 

 hydrolysis alkali was credited with powers of saponification. 



Hirsch, in 1898, showed experimentally that fatty oils were not 

 more readily emulsified than were various other organic liquids, 

 and he demonstrated also that the large amount of oil emulsified 

 was quite out of proportion to the small amount of soap present. 

 This showed that the effects produced were ascribable to the soap 

 itself and not to any alkali present. 



Donnnan {Zeitsch physical Chem., 1899, 31, 42) showed experi- 

 mentally that emulsification and lowering of surface tension went 

 hand in hand in the case of solutions of different soaps. Plateau had 

 pointed out that in general formation of solid surface films might be 

 quite as effective as low surface tension in emulsification. 



HiUyer {Jour. Amer. Chem. Soc, 1903, 25, 511, 524, and 1256) 

 showed experimentally that the emulsifjdng properties of soap could 

 not be attributed to hydrolysis alkaU hydroxyl ions, nor did alkali 

 possess the power of wetting oily matter that soap did. Hence both 

 these factors in detergent action must be due to the soap itself. Of 

 course, as Donnan had pointed out, the free fatty acid contained in all 

 natural fats and fatty oils could be neutralised with formation of soap 

 this would be quite different from saponification of glycerides which is 

 an extremely slow reaction. HiUyer demonstrated again the parallelism 



