1 8 PROTOPLASM 



rected by mixture with some that is too fluid. I have 

 usually improved to some extent my samples of oil in this 

 fashion. 



I will not report here in more detail upon the numerous 

 experiments which preceded the discovery of the above described 

 method. Since it seemed an obvious hypothesis that the free 

 oleic acid mixed with the oil must be of influence upon the 

 formation of soap and froth, I attempted to improve the unser- 

 viceable ordinary oil by addition of a few drops of pure oleic 

 acid; but this addition, as well as that of a volatile oleic 

 acid (valerianic acid), proved quite useless. The attempt to 

 obtain a utilisable product by dissolving mutton-suet in the 

 olive oil met with just as little success ; nor was the olive oil 

 rendered any more serviceable after separation of the more 

 easily congealed glyceride by means of a freezing mixture. 



As to other oils I experimented with almond oil, boiled 

 linseed oil, cod-liver oil, and refined bone-oil (watchmakers' oil, 

 so-called). All the oils mentioned are more or less serviceable 

 when they possess the proper consistency ; but since, however, 

 they offered no special advantages, I usually returned again to 

 olive oil. Furthermore, the manufacture of froth-drops with 

 Na 9 C0 3 and NH 4 NH 2 C0 2 was tried ; but the experiments were, 

 as a rule, more successful with K 2 CO 3 , on which account this 

 salt alone was finally employed. At the commencement I used 

 carbonate of potash finely pulverised, and freed as far as possible 

 from water ; later, however, I convinced myself that the experi 

 ments succeed better if the salt is slightly damp. Hence I 

 proceed now to breathe several times on the small sample of 

 salt, while pounding it in the mortar, till it is moderately damp, 

 and then to rub it up well with the drop of oil into a thickish paste. 

 This paste is immediately made further use of in the way described, 

 since after standing long it loses its valuable properties. Little 

 feet of paraffin serve for the support of the corners of the cover- 

 slip in these experiments, since wax, or cobblers' wax, becomes 

 friable under the action of the K 2 C0 3 solution, which is gradually 

 formed under the cover-slip. 



The processes which go on while such a drop of paste placed 

 in water, is converted into foam are, as far as they can be 

 observed under the microscope, somewhat as follows. The 

 drops of the paste when in the water pass into more or less 

 violent undulatory movements, since here and there particles 

 of K CO pass from the paste into the surrounding water, 



