"The 'moss' has given me no trouble at all this winter; in fact, I have for six months had to resort to the copper sulphate only once.... All the conditions were favorable last fall and early winter for a riot of 'moss,' but it did not appear at all until just a few days ago, and then yielded to treatment much more readily than it did when I first began to use the copper." This letter was written over three years after Dr. Moore made his experiment in these cress beds.
Satisfied with the results attained in exterminating algal growth in water-cress beds, attention was next given to reservoirs. Some fifty water supplies were treated during the summer of 1904, and in every case success attended the copper cure. In one respect the results were surprising. It was found that in practice the copper-sulphate method worked better than in theoretic experimentation; results in large reservoirs were more pronounced than in the laboratory. In fact, it developed that the solution necessary to kill algæ in the laboratory must contain from five to twenty times as much copper as that contained in a solution which will exterminate algal growth in its natural habitat. This is not easily explained, if it can be explained at all. The test reason advanced is that only the most resistant organisms stand transplanting to an artificial environment. But, after all, the important point is that the new method works better in practice than was expected.
A Prescription for the Copper Cure
Thus the department is able to announce that the process is no longer in the experimental stage, and also to say what conditions must be known in determining the proper quantity of copper sulphate for destroying algæ, together with a prescription for the copper cure. Here it is, for the benefit of careful persons who will use the method with proper intelligence: "The importance of knowing the temperature of the contaminated water is second only to the necessity of knowing the organism present. With increase of temperature the toxicity of a given dilution increases, and vice versa. Assuming that 59° F. is the average temperature of reservoirs during the seasons when treatment is demanded, the quantity of copper should be increased or decreased approximately 2.5 per cent for each degree below or above 59° F.
"Similar scales should be arranged for the organic content and the temporary hardness of the water. With the limited data at hand it is impracticable to determine these figures, but an increase of 2 per cent in the quantity of copper for each part per 100,000 of organic matter and an increase of 0.5 to 5 per cent in the proportion of copper for each part per 100,000 of temporary hardness will possibly be found correct. The proper variation in the increase due to hardness will depend upon the amount of dissolved carbon dioxide; if very small, 5 per cent increase is desirable; if large, 0.5 per cent is sufficient."
The information in this prescription is to be used in connection with a table[2] published by the Department of Agriculture. This table gives the number of parts of water to one part of copper sulphate necessary to kill the various forms of algæ which are listed. The formulæ vary from 1 part of copper to 100,000 parts of water, necessary to destroy the most resistant and very rare forms (three of these are listed), to 1 part of copper in 25,000,000 parts of water, which is a sufficiently strong solution to exterminate Spirogyra, the cress-bed pest. By far the majority of forms do not require a solution stronger than that of 1 part of copper to 1,000,000 parts of water.
What the Agricultural Department is Doing
It is true that the department is not now holding out, directly, a helping hand to the owner of a country place, or to the farmer, in this campaign of purifying drinking water. In the first place, the greatest good of the greatest number demands that large reservoirs, which supply a great number of people with drinking water, ought to be considered first. Such supplies, moreover, are most frequently contaminated. Where fifty reservoirs were treated last summer, ten times that number will be "cured" this summer. It will be readily seen, therefore, that in conducting such a large number of experiments—considering preliminary reports, prescribing for treatment, and keeping proper account of results—the department, with a limited force and limited facilities, has its hands more than full.
More important still, there is an absolute need of the services of some expert on the ground. While an algologist is a functionary not generally employed by water companies—in fact, a man trained in the physiology of algæ is difficult to find—nevertheless, it is highly important, as the department views it, to have the coöperation of an expert versed to some extent in the biological examination of drinking water. In other words, the copper cure is not a "patent medicine," with printed directions which any person could follow. Intelligence and care are absolutely essential in the use of this treatment. Furthermore, each case must be treated as a distinct and separate case, as a physician would treat a patient.