340 
had been previously employed by others. Nos. 2, 18, 19, 20, 21, and 22 
were first prepared by Mr. Galloway and Mr. Swingle in experiments 
with wheat rust at Garrett Park, Md. 
As it seemed advisable to adopt some arbitrary standard with which 
a comparison of the different substances could be made, it was decided 
to take as a standard the proportion of one part by weight of the metal 
forming the base of the salt to 1,000 parts of water. In the copper 
preparations it is 1:1,000; in the iron and zinc compounds. 2:1,000. It 
must not be supposed, however, that these are in all cases chemically 
accurate, since the substances used were not chemically pure and the 
water was not distilled. The same conditions prevailing, however, in 
each preparation it is thought that the comparative strengths are the 
same. One gallon of water was calculated to weigh 3,783 grams, and 
3.78 grams of copper or 7.56 grams of zinc or iron, generally in the form 
of a sulphate, were used in the preparation of the mixtures. The pro¬ 
portion of the atomic to molecular weight gave the required weight of 
the salt to be used. In the preparation of the fungicides another point 
was kept constantly in view, viz, that no substance not in the finest 
possible state of division should be sprayed upon the seedlings. In 
order to secure the chemicals in this condition it was necessary to pre¬ 
pare precipitates and apply them before they became dry. 
It has been found that dry, insoluble copper compounds, like cupric 
carbonate, when mixed with water do not split up into their smallest 
components, and hence do not adhere to the foliage as tenaciously as 
freshly prepared precipitates of the same substances. As will be 
inferred from the above, the preparation of each chemical necessitated 
the use of two or more ingredients, one the salt of the metal and the 
other an alkaline salt. With four exceptions the substances were all 
insoluble compounds, and by numerous titrations the optimum propor¬ 
tion of the salt containing the metal to that containing the alkali was 
established. By optimum is here meant that proportion which gave 
the lightest and most flocculent precipitate. Of two precipitates of 
the same salt, other things being equal, that one which remains 
longest suspended in the water is, according to the writer’s idea, best 
suited for a fungicide. A rapidly settling fungicide is to be avoided if 
possible. 
A test with potassium ferrocyanide was made to ascertain if any 
cupric sulphate remained in solution. As explained subsequently, there 
was present in all the mixtures a soluble salt, resulting from the com¬ 
bination of the alkali with the acid of the metal salt. This is indi¬ 
cated by the notes given after the name of the fungicide. 
The plan of the experiment was made as simple as possible. Twenty- 
five substances mixed in water were applied to 50 rows of seedlings, 
that is, each substance was applied to 2 rows. These rows did not 
stand side by side, but were separated by at least 60 feet. On each 
side of every treated row stood an untreated one to serve for compari- 
