MYELIN FORMS 



109 



{b) On adding a powdered neutral salt to a soap solution the 

 soap is " salted out " as a curdy mass. The salt reduces the 

 hydrophilie powers of the soap and so reduces the stability ol" 

 the dispersoid. This is a different phenomenon from the precipi- 

 tation of a colloid by electrolytes. 



(c) On adding a soluble salt of calcium or magnesium to a soap 

 of aumioniiuii, sodiiuii or potassium a curdy precipitate is produced. 

 This curd is a calcium or magnesimii soap, which, as we have seen, 

 has little or no aflinity for water. 



{d) Solvents of soaps added to a water-soap dispersoid lead to 

 a partition of the soap between 

 solvent and dispersion medium. 

 The effect of the anaesthetics on 

 soap sols, is interesting. Alcohol 

 brings about a rapid separation 

 of soap and water, practically all 

 the soap dissolving in the alcohol. 

 Chloroform has much the same 

 effect, but the partition is not so 

 complete. To get anything like 

 a complete extraction large 

 amounts of chloroform must be 

 used. Ether has hardly any 

 effect. 



Soaps have a powerful effect in 

 lowering surface tension, which 

 effect is greatly increased by the 

 addition of small quantities of 

 alkali (Shorter and Ellingworth). 

 A stalagmometer reading of oil 

 dropping into water was 65 drops. When 1 per cent, soap was 

 added to the water the drops increased to 260 (Hatschek). 



Myelin Forms. — If a drop of a soap of an unsaturated fatty acid 

 is allowed to come in contact with a drop of water, the soap will be 

 partially dissociated into base and fatty acid, and so cause a re- 

 arrangement of the internal structure of the fat droplet. The 

 visible sign of this alteration is the shooting out of a knob of 

 material into the water. Close examination of this extrusion 

 reveals that it is a coiled structure (Fig. 26 {a) ) with a distinct 

 adsorption membrane at the water-soap interfaces. If a micro- 

 polarimeter is used the coils will appear brightly coloured and 

 marked with a cross which rotates with the Nicol prism. One 

 associates this appearance with the fornuition of acicular crystals, 

 and, under the high power, bipyramidal crystals may be seen lying 



— Successive jiliases in tlic dcvelop- 

 inent of myelin outgrowths from a streak of 

 lecithin in n'lOO hydrochloric acid. (Courtesy 

 of Professor l^eathcs.) 



