518 ANNUAL REPORT OF THE Off. Doc. 



The materials composing Bordeaux mixture are both staple market 

 articles, aud in commerce are pure enough for all practical purposes. 

 The sulphate is marketed both as large and small crystals, but for 

 epru^'ing purposes the small crystals are just as good as the large. 

 The only adulteration which need possibly be feared is the admixture 

 of iron sulphate — copperas. So far as known, however, copper sul- 

 phate adulterated to any serious extent has never been found in 

 the regular market. 



Lime is more variable. In some localities it is unavoidably pre- 

 pared from a very poor class of rock. When such lime has to be 

 used in making Bordeaux mixture more has to be put in than when a 

 lime of good quality can be obtained. But the quantity of lime 

 should never be gauged by measure alone, for it is so essential that 

 enough be used "to neutralize" all of the copper sulphate, that the 

 mixture should be tested with either of the two simple tests at com- 

 mand to determine this point with certainty. A solution of 

 potassium ferrocyanide, yellow prussiate of potash (1 oz. dis- 

 solved in about a pint of water), is perhaps the most conveni- 

 ent test for determining the presence of sufficient lime. A 

 few drops of this solution added to a mixture containing 

 insufficient lime will produce a reddish brown discoloration, 

 while when sufficient lime has been added no discoloration 

 will result. In making this test it is best to dip out a small 

 quantity in a white saucer or shallow dish. Any slight discoloration 

 will then be readily seen against the white dish, which would not 

 be visible if the test were made by pouring the ferryocyauide solution 

 into the spray tank. The mixture should be thoroughly stirred be- 

 fore applying the test, and in order to be certain that it is, it is also 

 best to make two tests, giving a vigorous stirring between them. 

 The writer has sometimes found the second test to be different from 

 the first. When the two are alike it is safe to presume that enough 

 lime has been used. In using the ferrocyanide it must not be for- 

 gotten that it is a virulent poison. The utmost care is therefore nec- 

 essary iu having the bottle properly labeled and out of reach of chil- 

 drer and careless xjersons. When large quantities of stock solutions 

 are made up one test will suffice for the whole amount on hand. That 

 is, the one test will indicate the proper proportion of lime to use for 

 the total quantities of stock solutions prepared. Another excellent 

 method i« "to standardize" the lime milk with the copper sulphate so- 

 lution by making a small quantity of test mixture. The method of 

 making this test and standardizing as given by the writer in Bulletin 

 C8 of the Illinois Experiment »Station is as follows: 



"Make up the stock solution of copper sulphate as usual, one 

 pound per gallon of water. Slake the lime, making of it a thin paste. 

 >>ow take one pint of the copper sulphate stock solution, dilute to 

 about a gnllon, and add to that small measured quantities of the 



