September, 1923 INDUSTRIAL A N D ENGINRERING CHEMISTRY 91 1

Chemistry in the Control of Plant Enemies New Achievements and Future Possibilities

By Walter Collins O’Kane

CROP PROTECTION INSTITUTE, DURHAM, N. H

OTHING is more important in human welfare than row, pours a cupful of kerosene into the pail, and knocks protection from the myriads of minute enemies in the beetles into this improvised device where the touch of a N the plant and animal world. In this chemistry is drop of the liquid will finish off the pest, thus saving time

now taking a leading part and is certain to make extraordinarv and energy and rendering his task more efficient. He has development.

By t,he very nature of the case this must be so. The whole tendency of man is to flock together, to subjugate the liv- ing world and make it yield sustenance, shelter, and all else. In vast areas this has been going on for hundreds, or even thou- sands, of years. In other widespacesit is only beginning. The tendency is as strong as human nature itself. and it is constantly assuming concrete shape.

So it is that the human race is the great upsetter of the natural balance in nature. We cut down forests, pull out the stumps, plow the land, and plant a hundred thousand acres of potatoes. We break up the sod of a million acres of prairie and seed it all down to wheat.

All this is necessary and, apparently, is going to continue and to increase. The same number of acres that supported a man and his family must come to sup- port a score or a hundred, who are working to make other things that the

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turned, ai-he should, to chemistrv.

WALTER COLLIN3 O’KANE

man and his family, and many others besides, want and need.

We cannot do this and expect natural forces to protect from harm the altered conditions that we have brought about in our fields and gardens. Amicroscopic, organism that would cause a rust spot on a wheat plant might blow about in the wind and never find a suitable plant, if wheat grew only as single, isolated specimens, scattered here and there in the midst of other vegetation. But that same microscopic organism developing on a plant in a thousand-acre Dakota field cannot fail to find a suitable host on which to develop. A beetle with black and orange stripes, hunting for wild potatoes in mountain highlands, may find the chances a thousand to one against it. But the same beetle in a Michi- gan potato field needs a dose of poison to put an end to its career.

The increased price of a product is bound to make it possible to spend money to raise i t successfully, if it is something that human beings need, or want, or think they want. There is no more doubt about that than there is about the rising of the sun to-morrow. And it is quite certain that the demand €or foodstuffs with which to support life, for the products that make life pleasurable, and even for those that bring luxury, is not going to fall off.

The means of avoiding losses from the various minute enemies can take many forms. At the beginning the methods are sure to be crude and laborious. The owner of the potato patch goes through it with a stick in his hand, knocks the potato beetles off onto the ground, and tramps on them. But presently he carries a pail with him as he goes down the

’ It is a long-step from this crude proc- ew to the spraying, dusting, and fumi- gating that are now helping us to raise crops. Rut it is not a long step in time. The last twenty years have seen the greater part of the development, and a period much shorter than that has wit- nessed a large proportion of the more important discoveries. The field is rela- tively new, as work in chemistry goes, and the progress that has been made is only a fraction of that which has been achieved in other lines where the de- mands of industry on the resources of the chemist were stronger.

Within these few years striking ad- vance has been made and materials have been developed that not only are impor- tant in themselves, but may rightly be taken as forerunners of the progress that is sure to follow. It is interesting and suggestive to consider some of these developments.

p-DICHLOROBENZENE FOR PEACH BORER

Take the peach borer, for example. There has been hitherto no satisfactory control of this pest. Recent work in New Jersey has shown that p-dichlorobenzene, applied in a ring near the trunk of the tree and covered with soil, affords efficient and economical control. Several hundred thousand trees have now been treated through two or three seasons and the method is a proved success. Other possi- bilities of the substance are now being studied.

SULFUR SPRAYS

Sulfur was one of the first elements ever to be used for the control of plant diseases. Within the memory of most of fis a chemical combination of sulfur and lime came into use as a spray to kill scale and to help control certain fungous diseases. But nobody knew precisely how the thing worked. It would act in certain fashion under one set of conditions, but in other manner under other circumstances. It was like a rifle that could shoot a bullet a long distance, but could not always be aimed, and sometimes missed fire.

Within the year much of this mystery has been cleared up and a possible means of controlling and enlarging the utility of sulfur has been discovered. It has been found that in the changes that lime sulfur undergoes after it has been applied as a spray, a new substance is formed which is the really active agent in control of plant diseases. Fur- thermore, ways have been found which promise to make it possible to control the formation of this substance and a t

912 INDUSTRIAL A N D ENGINEERING CHEMISTRY Vol. 15, No. 9

the same time to take lime sulfur out of the class of sprays that burn foliage and place it in the class of those that can be used quite safely in large amounts and in heavy concen- tration.

SODIUM FLUORIDE FOR ROACHES Among the oldest of insect pests, as the geologists measure

time, are the roaches. Prehistoric man may not have stayed long enough in one place to be bothered by them, but we know that they were in existence in those remote times quite as abundantly as they are now. There have been hundreds of roach powders, pastes, traps, and cures. Some of them do more or less good. But recently we have found in sodium fluoride a material that, rightly used, can eliminate roaches from overrun premises. The same material will kill ants. And so, probably for the first time in history, the human species can easily and securely rid itself of two prize nuisances in the insect world.

POSSIBILITIES OF MERCURY Plant pathologists are well aware that in handling certain

plant organisms in the presence of mercury they must protect them from the effects of its vapors. To what extent can this properly be utilized? How about its effects on animal organ- isms, such as insects? In parts of India there is a tradition that mercury, exposed in a tight container along with beans or other stored products on which the bean weevil has laid its eggs, will prevent these eggs from hatching. American experimenters have put this tradition to the test in recent trials and have found that the mercury does have a definite effect. The volatilization of the mercury is presumably very slow. A chemist’s balance would have difficulty in detecting the loss, except by exceedingly delicate measure- ments.

CONTROL OF CEREAL GRAIK SMUTS The smuts of cereal grains have offered a serious problem

to the expert in plant diseases. There was no mystery about the cause or the way in which they were carried. The diffi- culty lay in proposing a means of control that would be practical on a large scale. Two new measures are among the recent discoveries. The first of these turns to copper, a metal that has long been utilized in one way or another in fighting plant diseases. The other lies in the group of organic mercuric compounds that have been developed since the beginning of the World War.

NEW USES FOR CARBON DISULFIDE

Carbon disulfide, used for many years as a fumigant for grain weevils, is yielding new facts as a result of further study, backed by vision and resourcefulness. An experi- menter, finding mosquito wrigglers abundant in a tub of stagnant water, dropped into it a teaspoonful of carbon disulfide. One would not expect any marked results, since the material is not soluble in water, except in slight degree. But in a minute or two the wigglers were in discomfort and in a few minutes more they were dead. The instance is suggestive. Other experimenters have tried an emulsion of carbon disulfide, greatly diluted with water, as a possible material for killing grubs a t work on grass roots. Curiously, they have found that moderate amounts of the material, thus emulsified and diluted, bring about a high percentage of kill.

INSECT BAITS AND REPELLENTS We have only begun to explore the possibilities that may

lie in the use of chemical compounds as baits for noxious insects, or as repellents. Every insect is a bundle of auto- matic reactions. Most of all, it is attracted or repelled by

odors. This response largely controls the movement of an insect in search of food and, therefore, has a great deal to do with its harmful activity. If we can place before it an effective poison and can add to our dose some compound that will prove sufficiently attractive, we may persuade the pest to partake of our offering. Perhaps we can attract it away from the plant or product that it would injure in its feeding, and persuade it to eat something that is valueless while a t the same time working its own destruction. Thus, amyl acetate has been found to serve as an attractive in- gredient in a poison bait for grasshoppers.

The corn-ear worm has a wide range of food plants. The adult that lays the eggs from which the worms hatch is attracted by corn silk. In- vestigators have taken strands of cotton twine, soaked them in the juice obtained by crushing corn silk, and have attracted the moths to these strands. By studying the composition of the silk, isolating the active principle that .attracts the moths, and then seeking the aid of chemistry to devise a substance that will simulate this principle, it may prove possible to devise a poison bait for this destructive pest that will protect our vast cornfields from the tremendous damage that they now suffer because of it. If this can be done, as appears not a t all impossible, we may be able to follow a similar procedure with reference to many other devastating pests.

What shall we use as a poison? For many years our principal reliance has been placed on arsenic in one or another of its compounds. But we have reason to believe that the toxicity of various arsenical compounds to insects is by no means in direct proportion to the amount of arsenic that the com- pounds contain. Work is now in progress which is intended to throw light on this question, to help us to learn what forms of arsenic become most toxic within the digestive tract of insects and what influence may be exerted by the physical character of the material.

We have observed, a t times, that some insects appear to be repelled by the presence of arsenical poisons on the plants on which they were feeding. Recent work with a new invader, the Japanese beetle, goes to show that so far as this insect is concerned the repellent effect is probably due to the discomfort caused by the irritating character of the first minute amounts of poison eaten. Investigators have tried the experiment, of administering with the poison spray an intestinal sedative, such as bismuth subcarbonate. Bee- tles fed on this mixture ate more of the poisonedleaves; more of the beetles consumed a fatal dose. Administration of bismuth subcarbonate on a large scale would not be prac- ticable. But the principle involved is interesting and im- portant.

But that is only a beginning.

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But the work and the possibilities do not end there.

CONTROL OF THICKNESS OF SPRAY There is a big question, which experimenters are only

beginning to touch on; that involves the addition of neutral or subsidiary materials to a spray in order to render it more effective through altering its physical qualities. With their assistance it may be possible to control, not only the covering qualities of a spray, but the thickness of the film deposited and its adhesive qualities. Conceivably, we may come to say, before long, that protection of apple foliage from a certain invading plant disease will require a film so many microns in thickness persisting through so many days, that less than this will be ineffective, and that more will be a waste of material.

EFFECT OF MIXTURES Most of our spray schedules nowadays call for mixtures

We need to apply materials that will accom- of this or that.

September, 1923 INDUSTRIAL AND ENGINEERING CHEiMlSTRY 913

plish more than one purpose and it is highly advantageous to do this in one operation. However, this turns the spray barrel into a chemical laboratory. Because Ingredient A is effective for one purpose and Ingredient B for another, it does not follow that A and B mixed together will retain their valuable characters in full degree, or even a t all. They may, instead, gain a new character that makes them highly harmful. The sprays to be worked out for the future must be devised, not only with reference to their individual quali- ties, but with reference' to their compatability one with an- other.

UNSOLVED PROBLEMS In many of the new fields of inquiry we cannot even lay

claim to a good start. Early blight once started in a potato field can, and sometimes does, sweep through it so rapidly that the ordinary grower, aware of the existence of the disease only when it has gained headway, cannot stop it before it has utterly destroyed his crop. The plant pathologist, taking it in time, can spray and check it. Rut what can we offer the grower that will prevent infection?

A recent list prepared by a committee of plant pathologists gives more than a hundred plant diseases carried by seeds.

More than fifty of these are endophytes living within the substance of the seed. Some of these diseases take enormous toll of our crops. How shall we treat seeds on the large scale in which they must be handled in farm practice and sterilize them successfully?

Investigators have worked diligently to discover the cause of the mosaic diseases affecting various plants. We do not yet know what the cause may be. Without this knowl- edge we are badly handicapped in our search for means of control.

In certain sections of the East a serious plant enemy has become established, known as the potato wart disease. About the only recommendation that can be offered the grower is to change to varieties of potatoes that have been found to possess more or less resistance. We need to discover a defi- nite and specific means of solving this and other equally unsolved problems.

Nine times out of ten, perhaps ninety-nine times out of a hundred, our constantly increasing reliance in all this must be placed on discoveries in chemistry, working in intimate alliance with the biological sciences, with plant pathology, entomology, and bacteriology. It is an enormous field and the possibilities are equally tremendous.

Using Excess Power to Save Coal Electrical Generation of Steam for Heating and Process Work

By E. H. Horstkotte

GENERAL ELECTRIC Co., SCHENECTADY, N. Y.

FF-PEAK periods of demand for power on idle days when plants are shut down and Sundays and holidays 0 often present important problems in fuel economy to

plant engineers who are obliged to keep steam on the system for heating or other purposes. Heretofore, it has been necessary to keep at least one fuel-fired boiler in action, with the attendant expense of firemen, to say nothing of the fuel consumed. Textile mills, chemical plants, manufacturers of pulp and paper, and other industries, including central stations from whom such plants purchase power, if they do not make it themselves, are alike affected by this problem.

DESCRIPTION OF GENERATISG PLANT The recent development of practical and economical means

for the electrical generation of steam is affording an interesting solution to this problem of fuel economy through the use of an electric steam boiler which in effect may be said to form a complete steam-generating plant capable of operation with minimum attendance.

The complete equipment consists of the shell with support- ing feet, the electrodes, insulators, steam and water gages, safety vdve, circulating pump and motor, and a panel on which is mounted the control equipment (Fig. 1).

The tank, or generator shell, is mounted vertically, and divided horizontally into two compartments, the upper known as the electrode compartment, where the actual generation of steam takes place, and the lower forming a self-contained hot well. Water entering the hot well from the feed-water pipe is forced into the upper chamber by a motor-driven centrifugal pump located on a short external pipe linc. From this chamber it flows back into the hot well through a number of small holes on the outer circum- ference of the dividing plate. This arrangement provides

a continual circulation of heated water, the water level in the electrode chamber being held a t the desired level by setting the valve in the circulating pump discharge line.

The upper, or electrode chamber, where the steam is gen- erated, contains three large, round, iron electrodes rigidly supported from the roof, the current-carrying supporting rods coming in through specially designed insulating bush- ings. These bushings are provided with a small duct in the top leading to the outside air. Thus, if steam does succeed in leaking through the packing into the upper section of the bushing, it passes out freely instead of creating a pressure that might blow out the side of the insulator.

The electrical operation resembles that of a three-phase arc furnace. Normally, the electrodes are submerged in the water, and the three-phase current passes through the water to the sides of the tank, or from electrode to electrode. The steam is generated by current flowing through the water, which is of high resistance. The temperature of all the water in the system is practically uniform. If the steam pressure lowers owing to an increased demand, rapid steam generation due to the high temperature of the water and the degree to which the electrodes are submerged quickly brings the pres- sure up again.

Another operating feature is that since the water level is maintained by the adjustment of the throttle of the circu- lating pump, the energy consumption of the generator is not dependent on the operation of the feed-water pump. The supply of water in the hot well is regulated by an auto- matic feed-water regulator. Furthermore, when it is desired to reduce the load, the generator does not have to be blown, which means that water does not have to be pumped in subsequently against full pressure. The only energy losses in the circulating pump are the motor losses and the pump