April 17, 1895.] 



Garden and Forest. 



159 



As only about two dozen plants in a house of ordinary size 

 behaved tliis way, it is Hkeiy that some plants have a greater 

 tendency to throw roots than others or were more favorably 

 situated, or both. 

 Rutgers College. Byroti D. Halstcd. 



The Preparation of Bordeaux Mixture. 

 To the Editor of Garden and Forest : 



Sir, — The Patrigeon method of preparing the Bordeaux 

 mixture was first published in the spring of 1890.* Tlie direc- 

 tions were to add the milk of lime to a solution of copper sul- 

 phate until a twenty per cent, solution of the ferrocyanide of 

 potassium would show no discoloration when added to the 

 mixture. This process soon became known in America, and 

 we find the following directions for preparing the fungicide : f 



" The copper sulphate is weighed and mixed with an amount 

 of water sufficient to dissolve it. When it is completely dis- 

 solved, the lime, in the form of thin whitewash, is strained 

 through burlap (gunny sacking) into the copper sulphate solu- 

 tion. A drop or two ot potassium ferrocyanide (saturated aque- 

 ous solution) added from time to time, after thoroughly stirrmg 

 the mixture, will show when enough lime has been added to 

 form the Bordeaux mixture. It not enough lime has been used 

 the drop of ferrocyanide will turn to a very dark color the mo- 

 ment it touches the mixture ; if enough lime has been used 

 the ferrocyanide will not change color when it is dropped 

 into the mixture." 



The substance of the above extract was repeatedly pub- 

 lished, and it appeared as late as the summer of 1894. \ Users 

 of the test have been at the same time cautioned to use a suf- 

 ficient amount of lime, since an excess would do no harm to 

 foliage. But in no case has it been advised to add an excess 

 ot lime, the amount called for by the test being sufficient, pro- 

 vided the preparation was well stirred and the proper care 

 exercised in the use of the test. Yet in the fall of 1894 we find 

 that the original formula is no longer unconditionally recom- 

 mended, but that "a little more lime should be added after 

 tills test shows no color," in order that there may be no doubt 

 that enough shall be present. | 



The question now arises, why is lime added to the Bordeaux 

 mixture after the immediate demands of the ferrocyanide test 

 have been satisfied ? The following considerations may help 

 us to find the correct answer : 



(i) When the milk of lime is added to a solution of copper 

 sulphate, the latter is broken up and new compounds are 

 formed. The lime is not added merely to neutralize the acidity 

 of the solution, but a sutficient amount should be present to 

 satisfy all chemical changes. But all these clianges do not 

 appear to take place at once ; "so it occasionally happens that 

 after the mixture has been standing a few minutes the potas- 

 sium ferrocyanide will again give the dark color, showing that 

 not enough lime had been added." || It is an undisputed ques- 

 tion that a sufficient amount of lime must be added to prevent 

 any of the copper sulphate from remaining in solution, other- 

 wise the foliage of nearly all plants will sustain injury. Yet 

 the Bordeaux mixture, when prepared according to the origi- 

 nal directions of Patrigeon, is not supposed to contain an 

 excess of lime ; in fact, the value of the test rests in its power 

 to detect just when no more lime is needed. 



(2) That foliage is occasionally injured by the Bordeaux 

 mixture when prepared with the minimum amount of lime 

 cannot be doubted, for injury has followed the use of the 

 mixture when it contained considerable quantities in excess. 

 No definite experiments appear thus far to have been made 

 for the purpose of comparing the action of the Bordeaux mix- 

 ture when prepared witli the ferrocyanide test, and that made 

 in accordance with the commonly accepted formulas. Fair- 

 child, who has made a special study of the Bordeaux mixture, 

 was in doubt regarding the advisability of accepting I^atri- 

 geon's method without further experimentation. He says :^ 

 " It is possible, also, that pathologists have proceeded too rap- 

 idly in recommending the use of potassium ferrocyanide in the 

 preparation of this mixture. It has not yet been definitely 

 settled that the mixture, when prepared according to this 

 method, will not contain the basic sulphates and occasionally 

 prove injurious. In attempting to avoid the inconvenience in 

 the preparation of Bordeaux mixture the greatest care must be 

 taken that its real value is not impaired. The excess of lime 

 in the mixture, instead of being an injurious element, may 



* Patrigeon, yournal d'Ag-j-i'culiityc, Prat., i8go. May i5tli, p. 701. 

 t Beach. Annual Report New York Agricultural Ex|jeriment Station, 1S92, p. 539, 

 X New York Agricultural Experiment Station, 1S94. fune Bulletin 72, p. 346. 

 § New York Agricultural Experiment Station. September Bulletin 74, p. 404. 

 II New York Agricultural Experiment Station, 1894. September FJulletin 74, p, 404. 

 i[ Bordeaux Mixture as a Fungicide. U.S. Department of Agriculture, Division 

 Vegetable Pathology, 1894. Bulletin 6, p. 14. 



prove beneficial, preventing injuries from the copper salt, and 

 in other ways being of advantage." Professor Bailey, after 

 extended observation throughout this state during the past 

 season, has come to the following conclusion:* "This test 

 indicates when sufficient lime has been added to correct the 

 present injurious effects of the sulphate of copper ; but in wet 

 seasons — if, in fact, not in all seasons — an extra amount of 

 lime may be needed to neutralize subsequent changes in the 

 compound. I am strongly of the opinion that the regular 

 formula for the Bordeaux mixture ... is the safest and best 

 one." My own experience has shown that the most serious 

 cases of the rusting of apples have been in orchards treated 

 with the Bordeaux mixture, prepared with the aid of the test 

 the applications having been made in orchards about Ithaca' 

 and also in the western part of the state. At Ithaca we had 

 orchards containing the same varieties- for comparison, the 

 one having been sprayed with Patrigeon's Bordeaux mix'ture 

 the other with that made according to a formula. No definite 

 data can be given, but the impression received from the ex- 

 amination of the two orchards was unfavorable to the use of 

 tlie test ; so much so that a considerable excess of lime was 

 added when the mixture was prepared the second time. 



(3) The chemistry ot the Bordeaux mixture, as now'under- 

 stood, indicates that more lime is necessary than the ferrocya- 

 nide of potassium test demands. Abundant experimentation 

 has shown that the carbonic acid found in rain and dew exerts 

 a solvent action upon the copper compounds found in the 

 mixture whenever no excess of lime is present. In other 

 words, the greater the excess of lime in the Bordeaux mixture 

 the more slowly will the copper compounds lje dissolved, and' 

 therefore, the smaller the excess the more quickly will the copper 

 enter into solution. The solvent action of the water is o-reater 

 where there is much dew or where the rainfall is more "or less 

 continuous. Light rains and a moist atmosphere will dissolve 

 the copper most readily, and the solution will collect upon the 

 foliage unless the raintall is sufficiently violent to wash it off. 

 Which form of the copper is most readily dissolved from the 

 mixture is uncertain, but Willard has suggested that the solu- 

 tion contains considerable quantities of the sulphate of copper, 

 a compound which is known to be caustic to foliage. f Such 

 conditions very readily explain the injury done by the Bor- 

 deaux mixture in 1894, and also the increased injury following 

 the adoption ot Patrigeon's method of making it. '^ 



(4) The Bordeaux mixture is now frequently applied with 

 Paris green or London purple. These poisons are unsafe to 

 apply to the foliage of many plants unless lime is added to the 

 liquid. But if the Bordeaux mixture does not contain an ex- 

 cess of lime, injury may follow the application of such a com- 

 bination, especially in a wet season. When Patrigeon's method 

 is recommended, special direction should be given for cases 

 in which arsenites are to be used with the fungicide. 



(5) A serious objection to relying upon the ferrocyanide test 

 is the danger arising from its improper use. This was clearlv 

 shown in the article of Professor Beach on page 128 of the cur- 

 rent volume of Garden and Forest. Serious injury may 

 follow, and appears to have followed, from such mistakes. 

 When a definite formula is employed there is less liability of 

 error, and, to my knowledge, no preparation has proved itself 

 safer, when the proper ingredients are used, than the formula 

 given below. 



Color tests possess a decided value in the preparation of the 

 Bordeaux mixture, since they mark a certain stage in the 

 preparation of the compound. The color of the mixture itself 

 also shows the same, f have frequently made this fungicide 

 without the aid of scales or of the lerrocyanide test, basing the 

 amount of lime added upon the color of the mixture. The use 

 of the test is safer, however, and if a sufficient excess of lime 

 is added the preparation must be as effectual and as safe as if 

 the ingredients had been weighed. But this excess of lime is 

 an uncertain quantity, and as a general recommendation I 

 should prefer six pounds of copper sulphate, four pounds of 

 quicklime and forty to fifty gallons of water as the safest pro- 

 portions. I have used the formula for three years, partly be- 

 cause the fungicide was used in experimental work and a 

 definite compound w\s desired; in other cases the ferrocya- 

 nide test or the color test of the mixture served as a guide to 

 the proper amount of lime. During this time I have not once 

 strained either the lime or the Bordeaux mixture, since in 

 making the application no trouble was experienced from the 

 clogging of machinery. The iMcGowen nozzle has been used 

 almost exclusively. With the Vermorel nozzle it may be ad- 

 visable to strain the lime in the majority of cases, altho'ugh not 

 necessarily more because the latter is weighed. The weigh- 



* Cornell Agricultural Experiment Station, iSa4. October Bulletin 74, p. 3S3. 

 t Cited by Kairchild, Bordeaux Mixture as a fungicide, page 14. 



