272 THE MONTHLY BULLETIN. 



glycerin is a weak base, so that when the conditions are right, the potas- 

 sium or sodium of a lye will replace the glycerin of a fat or oil and enter 

 into chemical combination with the fatty acids. Now this is just what 

 happens in the process of soap making. (In the case of rosin, oleic 

 acid, etc., these substances have no base, but are of an acidic nature 

 and will unite directly with the alkali bases to form a soap.) A soap. 

 then, may be considered to be a fat or an oil in which the weak base, 

 glycerin, has been replaced by a stronger metallic base. Now it 

 happens that the only soaps which will dissolve in water are the potas- 

 sium and sodium soaps. Soaps of the other metals (such as lead, lime 

 or copper soaps) are also readily formed, but these are all gummy, 

 sticky masses, entirely insoluble in water and unsuitable for the 

 preparation of spray mixtures. 



Furthermore, if any soluble form of lead, lime, copper, iron or any 

 of the metals except potassium or sodium comes in contact with a dis- 

 solved soap, the soap is broken up and an insoluble soap is formed 

 corresponding to the metal — that is, a lead, lime, copper, iron, or other 

 insoluble soap. These soaps of the non-alkali metals, being insoluble in 

 water, form a curd and are of no value as detergents or for spraying. 



A familiar instance of this kind is the "curdling of water" when 

 soap is put into hard water. The hardness of water is usually due to 

 some soluble salt of lime or magnesia, and when these come in contact 

 with the soluble soap, the insoluble lime or magnesia soap is formed 

 and is the "curd" of hard waters. 



Soaps-lime-sulfur. The "curdling" of hard waters, just alluded 

 to, is precisely the same kind of a change that takes place when soap 

 is added to lime-sulfur solution. An insoluble lime soap is formed 

 that destroys the usefulness of the mixture. Practically all of the 

 sulfur will be thrown out of a lime-sulfur solution by this treatment. 

 The new compounds are not especially dangerous to use, but are apt 

 to clog the spraying apparatus and the sulfur is no longer evenly 

 distributed throughout the liquid. 



Emulsions-lime-sulfur. If the emulsion is a soap emulsion, the 

 soap of the emulsion will be broken up, as in the case of lime-sulfur, 

 and the emulsion destroyed, setting free the oil and precipitating the 

 .sulfur. There is present the possibility of foliage injury, due to the 

 uneven distribution of the oil. 



Soap-iron sulfid and soap emulsions-iron sulfid. These two com- 

 binations are incompatil)le, for much the same reasons as are the two 

 previous ones, but to a lesser degree. 



Tobacco-lime-sulfur. Compatible. 



Tobacco-iron-sulfid. Compatible. 



This completes the discussion of the main part of the table. For con- 

 venient reference, however, the general effect of the alkalies and acids 

 upon the various remedies is also indicated and will be gone over rapidly. 

 This part of the table is given with the idea that it may be of service as 

 a warning against some mistakes that might very easily be made, such as 

 pouring lime-sulfur into an "empty" vinegar barrel or working up 

 acid lead arsenate in a pot in which there is left the remains of the last 

 batch of .soap 



