tTNIVEBSITY OF CALIFOBNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA I. FUMIGATION WITH LIQUID HYDROCYANIC ACID BY H. J. QUAYLE II. PHYSICAL AND CHEMICAL PROPERTIES OF LIQUID HYDROCYANIC ACID BY GEO. P. GRAY AND E. R. HULBIRT BULLETIN No. 308 JUxVE, 1919 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1919 Benjamin Ide Wheeler, President of the University. EXPEEIMENT STATION STAFF HEADS OF DIVISIONS Thomas Forsyth Hunt, Director. Edward J. Wickson, Horticulture (Emeritus). Herbert J. Webber, Director Citrus Experiment Station; Plant Breeding. Hubert E. Van Norman, Vice-Director; Dairy Management. William A. Setchell, Botany. Myer E. Jaffa, Nutrition. Charles W. Woodworth, Entomology. Ealph E. Smith, Plant Pathology. J. Eliot Coit, Citriculture. John W. Gilmore, Agronomy. Charles F. Shaw, Soil Technology. John W. Gregg, Landscape Gardening and Floriculture. Frederic T. Bioletti, Viticulture and Enology. Warren T. Clarke, Agricultural Extension. John S. Burd, Agricultural Chemistry. Charles B. Lipman, Soil Chemistry and Bacteriology. Clarence M. Haring, Veterinary Science and Bacteriology. Ernest B. Babcock, Genetics. Gordon H. True, Animal Husbandry. James T. Barrett, Plant Pathology. Fritz W. Woll, Animal Nutrition. Walter Mulford, Forestry. W. P. Kelley, Agricultural Chemistry. H. J. Quayle, Entomology. J. B. Davidson, Agricultural Engineering. Elwood Mead, Eural Institutions. H. S. Eeed, Plant Physiology. J. C. Whitten, Pomology. IFrank Adams, Irrigation Investigations. C. L. Eoadhouse, Dairy Industry. Frederick L. Griffin, Agricultural Education. John E. Dougherty, Poultry Husbandry. S. S. Eogers, Olericulture. J. G. MooDEY, Assistant to the Director. Mrs. D. L. Bunnell, Librarian. DIVISION OF ENTOMOLOGY Citrus Experiment Station at Eiverside H. J. Quayle *A. F. Swain Hugh Knight Division of Entomology at Berkeley C. W. Woodworth G. P. Gray W. B. Herms S. B. Freeborn E. C. Van Dyke G. A. Coleman E. O. Essig H. H. Severin E. E. DeOng t In co-operation with office of Public Eoads and Eural Engineering, U. S. Department of Agriculture. * In war service. I. FUMIGATION WITH LIQUID HYDROCYANIC ACID^ By H. J. QUAYLE2 INTRODUCTION Liquid hydrocj^aiiic acid^ was first used largely in experimental tests in 1916 and on an extensive commercial basis in 1917 for the fumigation of citrus trees in California.^ The inauguration of this new method of fumigation has brought up a number of points on which information is needed. Among the more important of these from the standpoint of the grower and fumigator are : the killing efficiency as compared with the pot and machine methods of generation of the gas ; the diffusion of the gas under the tent ; effect of temper- ature and humidity on such diffusion ; possible injury to the fruit and foliage ; injury when the liquid itself comes in contact with different parts of the tree ; the action of the liquid on the tents ; the best methods of handling the liquid in the field ; the precautions to be observed in such handling; and the cost of the liquid method as compared with other methods of fumigation. An attempt is made in the following pages to give some information on these points as based on two seasons* experience with liquid hydrocj^anic acid. Other important questions related to the physical and chemical properties of the material are discussed in Part II of this bulletin. 1 Paper no. 58, University of California, Graduate School of Tropical Agriculture and Citrus Experiment Station, Eiverside, California. 2 Acknowledgment is made of the assistance of Mr. A. F. Swain in 1917 and Mr. Hugh Knight in 1918 in carrying on the experiments on which this bulletin is based. 3 Hydrocyanic acid (HCN) is a liquid, but since it has never been used until recently in this form for fumigation purposes it seems necessary, to avoid con- fusion, to add the superfluous word ''liquid". The term for the same material which has gained common practical acceptance is ' ' liquid gas, ' ' which appears to be still less desirable. Another name wlich would correctly apply is ''prussic acid. ' ' 4 Under the title ' ' Anhydrous Liquid Hydrocyanic Acid for Fumigation Purposes," Mr. C. W. Mally published an article in the South African Journal of Science for October, 1915, giving an account of fi^migation tests for the mealy bug, Pseudococcus capensis, on the grape. This is the first record of the use of hydrocyanic acid as a liquid for fumigation purposes that has come to our notice. 394 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Some of the first tests with cyanide fumigation for citrus trees in 1886 involved the use of a generator outside of the tented tree.^ This outside generator w^as soon discarded for earthenware pots, which were placed under each tree, and the pot method of generation was in use exclusively until the season of 1914, when the outside generator was again adopted. This portable generator,*^ however, was very different from the crude generator of 1886. It was known as the ' ' Owl Fumigating Machine, ' ''^ and this generator utilized for the first time a solution of sodium cyanide. During the last two or three years the portable generator known as the "Cyanofumer", an improved machine, has been widely used. These older methods promise to be largely, if not entirely, supplanted in the near future by the use of liquid hydrocyanic acid. NATUEE OF LIQUID HYDEOCYANIC ACID AND PEECAUTIONS TO BE OBSEEVED IN HANDLING IT Liquid hydrocyanic acid has been known to chemists for many years, but probably because of its instability and its very poisonous nature, as well as the heretofore little actual need thereof, it has not been manufactured on a large scale. It is a colorless liquid, less than three-fourths the weight of water, having a specific gravity of 0.6969 at 18° C. It is also very volatile and boils at a temperature of 26.5 C or 79.7 F.« Because of its very high volatility, hydrocyanic acid gas is rapidly given off from the surface of the liquid, and thus there is danger in breathing in an atmosphere close to an open container. More gas will be given off as the surface of the liquid is increased and also in higher temperatures. The greatest surface is provided, and hence there is greatest danger when the liquid is sprayed or spattered. If there is any appreciable movement of the atmosphere the operator is reasonably safe if he keeps to the windward side of the exposed liquid. In any operation giving the material an opportunity to vaporize, such as filling or emptying the machine or containers, the apparatus should ^ Morse, F. W., The Use of Gases against Scale Insects. Bull. 71, California Agricultural Experiment Station, 1886. G Gray, Geo. P., New Fumigating Machines. Monthly Bull. California State Commission of Horticulture, vol. 4, no. 2, p. 68. 7 This machine was invented by Mr. Wm. Din*;le of Los Angeles, and Mr. Dingle, together with his brother, Irwin Dingle, also deserve the credit fr^ the inauguration, on a commercial basis, of the use of liquid hydrocyanic acid. 8 The Cyanide Industry by Eobine & Lenglen, translated by Le Clerc, p. 16, 1906. FUMIGATION WITH LIQUID HYDROCYANIC ACID 395 be arranged so that it is unnecessary for the operator to hold any- thing in place, and thus to avoid danger. Since the vapor is inflam- mable, flame-lights should be kept away from near the exposed liquid. Liquid hydrocyanic acid should be kept as cool as possible, and under ordinary circumstances this can be done by surrounding the container with cloth or sacking which is kept continuously moist. The containers should be in the shade and preferably where there is a free circulation of air. If the liquid is spilled on the hands there is no danger (if there are no cuts or abrasions) from the actual contact of the liquid, though there may be danger from the gas given off. From our experience in the field, the most important precaution (and it would seem the most needless to mention) for^ operators to observe in the handling of liquid hydrocyanic acid is not to inhale in an atmosphere highly charged with the gas, and therefore to turn away when any liquid is exposed or get into the fresh air before inhaling again. For emergencies a gas mask may be a desirable part of the equipment of a fumigation crew. THE PLANT FOR THE MANUFACTURE OF LIQUID HYDROCYANIC ACID The first unit of the original plant for the manufacture of liquid hydrocyanic acid in California or elsewhere, on a commercial scale, is shown in figure 1. The process is comparatively simple. All that is necessary is to subject the gas, which is generated in the usual way, to a sufficiently low temperature, when it will condense even without pressure, or only such pressure as is exerted by the gas itself in the process of generation. The plant (see fig. 2) consists essentially of generators for the generation of the gas from sodium cyanide, sulfuric acid, and water, and a condensing system where the gas is conducted into numerous flues which are bathed in cold brine from the refriger- ation plant. The first product, which contains considerable water, is then distilled, which process separates most of the hydrocyanic acid from the water, yielding a product having a purity of 95 per cent or higher. The improvement possible in the present plant is to reduce the waste in the liquefaction process in order that a greater amount may be recovered from a given amount of sodium cyanide. During the past year approximately 80 per cent of the total cyanogen has been recovered, which is equivalent to about 14.8 gallons or 86 pounds of the anhydrous liquid from a case. The total weight of anhydrous hydrocyanic acid in a case of 200 pounds of sodium cyanide (51-52 396 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION per cent cyanogen) is 108 pounds.^ It is scarcely possible, commer- cially, to recover the total amount of 108 pounds from 200 pounds of sodium cyanide, although this amount will be more nearly approached as more improvements are made in the plant. r ' '- ■> • 4 * ^fl .^li *«--*;.v"'^? ' -^ , I'M III Fig. 1 — First unit of original plant for the manufacture of liquid hydrocyanic acid. Azusa, California. May, 1917. THE ATOMIZING MACHINE After the liquid is transported from the central plant to the field in proper containers it is placed in a machine, such as is indicated in figures 3 and 4. The atomizing machine consists of a tank holding two and one-half gallons of the liquid, a graduate for the measurement of the dosage, and a pump and spray nozzles for the atomizing of the liquid. By the upward stroke of the plunger, near the graduated scale (see fig. 4), the liquid is allowed to run into the graduate and by the downward stroke it is forced into the coil as shown. Then by the operation of the air pump on the right the liquid is forced out through nozzles at the end of the exit tube into a fine misty spray, which is immediately transformed into a gas. » See Table I in Part II of this bulletin. FUMIGATION WITH LIQUID HYDROCYANIC ACID 397 398 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION GEADUATION AND OPEEATION OF THE ATOMIZING MACHINE The atomizing machine in use during the season of 1918 was graduated on the basis of the recovery of 14 gallons of liquid hydro- cyanic acid from 200 pounds of cyanide; that is, the liquid recovered was made to go as far, according to our present schedules of dosage, as the original case of cyanide by other methods of generation. There are 3200 ounces in a case of sodium cyanide and 1792 fluid ounces Fig. 3 — Atomizing machine, in use season of 1917, for atomizing liquid hydro- cyanic acid under tent. in 14 gallons. This amount of fluid was therefore divided into 3200 parts, so that .560 fluid ounce was used as the equivalent of 1 ounce of the solid sodium cyanide. The actual amount of hydrocyanic acid in .56 fluid ounce of 95 per cent hydrocyanic acid may be calculated from the data in Table I, Part II, as follows : Fourteen gallons of liquid of this purity weighs 5.956 X 14 X 16, or 1334 ounces, but only 95 per cent of this weight is hydrocyanic acid, the remainder being impurities, mostly water. The amount of absolute hydrocyanic acid is 1334 X -95, or 1265.4 ounces. Dividing this by 3200, we obtain .395 as the weight in ounces of actual hydro- cyanic acid in the .560 fluid ounce of liquid delivered by the atomizer as the equivalent of 1 ounce of sodium cyanide. FUMIGATION WITH LIQUID HYDROCYANIC ACID 399 By other methods of generation, the pot and portable generator, we assume that about 90 per cent, at least, of the total gas is evolved.^^ Under this assumption, 1 ounce of sodium cyanide would yield a weight of .486 ounce of absolute hydrocyanic acid. If this amount were converted into a liquid containing 5 per cent of water the volume would be .693 fluid ounce. The dosage applied by the liquid system has been only 80 per cent of that applied by the older methods. If the same dosage is to be 'IHtf^*^1iwwi Fig. 4 — Atomizing machine in use season of 1918. applied, .693 fluid ounce of 95 per cent liquid (or .675 fluid ounce of 98 per cent liquid) must be used as the equivalent of the yield from 1 ounce of sodium cyanide when the gas is generated by the older methods. The above figures have all been given in the American system of weights and measures. More finely graduated cylinders can be ob- tained, marked in cubic centimeters and fractions, and are commonly used to test the accuracy of delivery from the atomizing machine. 10 H. D. Young, as reported in Circular 139 of the California Agricultural Experiment Station, determined that the Cyanofumer yielded, under the best working conditions, about 95 per cent of the total gas. It has usually been assumed that the yield from the pot method varied from 85 to 95 per cent. As a conservative average of both methods we have given, as above, a 90 per cent yield. 400 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The following metric equivalents will be useful in checking up their delivery. .693 fluid oz. = 20.5 c.c. (full dose of 95% HCN). .675 fluid oz. = 19.9 c.c. (full dose of 98% HCN). .560 fluid oz. = 16.5 c.c. (80% dose as applied last season). To insure proper dosage, it is important that the atomizing machine be kept in good working order. The machine should be emptied of the hydrocyanic acid after each night's run to avoid unnecessary action of the material on the parts of the machine, and the machine allowed to remain filled with water until it is used again. The machine should be tested frequently to see that the dose, as graduated, is delivered at the end of the exit tube. This is readily done by removing the nozzles and attaching a short piece of rubber tubing to conduct the liquid into a suitably marked graduate. If, for instance, an ounce on the graduate of the machine represents 16.5 cubic centimeters, when the machine is set for a 10-ounce charge there should be 165 cubic centimeters delivered into the graduate. A convenient graduate is furnished by running a 10-ounce charge into a long, narrow bottle and marking the height of the liquid by means of a file. Water may be used in measuring the accuracy of the pump, but there may be more water actually delivered than liquid hydrocyanic acid, so that it is more accurate to use the liquid itself, in which case the proper precautions regarding safety must be kept in mind. EFFECT OF LIQCTID HYDEOCYANIC ACID ON THE FRUIT AND FOLIAGE Gas from liquid hydrocyanic acid will injure the fruit and foliage if used in excess in much the same way as the gas generated by other methods. In many cases, however, particularly if the fumigation is done during low temperatures, the injury is often greater in the lower than in the upper half of the tree. This is accounted for under ''Diffusion of the Gas." When the liquid itself comes in contact with fruit or foliage severe burning occurs, as may be seen where the material is atomized in delivering the charge under the tent. This is not very serious, but in the case of much low-hanging fruit it is of some consequence. Such injury may be partly avoided by having a longer exit tube and ad- justing the nozzles to direct the spray at a smaller angle, so as to avoid the fringe of low-hanging fruit and foliage around the outside of the tree. There is no danger if the liquid strikes the trunk, at FUMIGATION WITH LIQUID HYDROCYANIC ACID 401 least of old trees. We have applied the spray directly to the trunk of two-year-old trees also without doing any injury. Possibly under conditions very unfavorable to evaporation, as during cold and wet weather, some injury might occur to the trunk of young trees. EFFECT OF LIQUID HYDEOCYANIC ACID ON TENTS One of the objections of the older methods of fumigation was the injury that was often done to tents. Liquid hydrocyanic acid has no effect on fabrics and there is no residue or acid anywhere around that may do such injury. COST OF USING LIQUID HYDEOCYANIC ACID AS COMPAEED WITH THE OTHEE METHODS OF FUMIGATION During the past tAvo years there has been little difference in the cost of using the liquid as compared with the other methods of fumi- gation. Distance from the manufacturing plant and other factors make the cost variable. However, when the manufacture of the liquid is better stabilized the cost of fumigation should be appreciably re- duced. Even if the actual material will not cost less, there will be a saving on the tents as well as less expense in handling the liquid in the field. When sodium cyanide (51-52 per cent cyanogen) is worth thirty cents per pound, the absolute liquid hydrocyanic acid would be worth fifty-five and five-ninths cents per pound. But it is not possible, commercially, to recover 100 per cent, and, moreover, the product recovered would not have a purity of 100 per cent. Neither is the cost of liquefaction included in the above price. If but 90 per cent is recovered in the liquid form, the corresponding price (solid cyanide at thirty cents) of the liquid would be sixty- two cents per pound. When a 90 per cent recovery contains 5 per cent water, the corresponding price per pound of the liquid would be be- tween fifty-eight and fifty-nine cents per pound. DIFFUSION OF THE GAS From previous experiments^^ it has been shown that with the gas generated by the pot or portable generator there is a greater concen- tration of the gas in the upper half of the tree, and consequently 11 Quayle, H. J., Cyanide Fumigation — Diffusion of Gas Under Tent and Shape of Tree in Eelation to Dosage. Jour. Economic Entomology, vol. 11, no. 3, p. 294, 1918. 402 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION better results on the scale insects in that part of the tree. "With the gas which arises from the liquid under present manipulations the conditions are exactly reversed and the better results occur in the lower half of the tree. Of the three locations — top, center, and bottom of the tree — the gas from the liquid is most effective at the bottom, next at the center, and least at the top. With the pot generation there is not much difference in effectiveness between the top and center of an average sized tree, but there is a decided decrease in effectiveness at the bottom. In field work the lower half of the tree is examined. The upper half, and particularly the top of the tree, is not examined unless some special effort is made. This fact is actually favorable to the results with the liquid and unfavorable to the results with the pots or port- able generator. But there are more scales, in most cases, in the lower than in the upper half of the tree. In 1917 an amount of liquid hydrocyanic acid equal to only 60 per cent of the total gas in a given amount of cyanide was compared with 90 per cent of the total gas from the same amount generated by the pot or portable generator. There was no difference in results by the ordinary field examination, but there was a marked difference in results by our own tests. In judging the results of the liquid as com- pared with other methods of fumigation in the field, therefore, allow- ance must be made for the necessary inaccuracy of tests under field conditions, and also for the fact that the examination is made in the lower half of the tree, where the liquid is more effective. The manner of diffusion of hydrocyanic acid gas is different according to whether it comes from liquid hydrocyanic acid or from a generator where the cyanide, sulfuric acid, and water are combined. In the former case, vaporization takes place near the ground and the gas gradually diffuses upward ; while in the latter the gas goes quickly to the top of the tree and gradually diffuses downward. This has been shown by the effects of the gas in first overcoming active insects at the bottom of the tree in one case and at the top of the tree in the other. And if the exposure is prolonged for an hour the final effect on the insects shows the same difference ; that is, in the latter case more recover at the bottom and in the former case more recover at the top. The manner of diffusion of the gas from the liquid, as explained above, is better adapted, we believe, to the killing of scales on the tree than the manner of diffusion from the pot or portable generator, particularly since most of the scales occur in the lower part of the tree, and for this reason it is possible that the liquid equivalent may FUMIGATION WITH LIQUID HYDROCYANIC ACID 403 be slightly reduced. The question may properly be raised whether more scales occur in the lower half of the tree because the older methods of fumigation failed to kill them as well there, but we believe that the habits of the insects also favor that location. EFFECT OF TEMPERATURE ON DIFFUSION OF HYDROCYANIC ACID GAS The question of temperature may be more vitally concerned with the diffusion of gas from the liquid than from the pot or portable generator, although it is a factor in any method of fumigation. The higher temperatures hasten the vaporization and diffusion of gas from the liquid and insure a better killing at the top of the tree. On the other hand, the higher temperatures aid in the diffusion of the gas downward with the pot method where it is first concentrated in the top of the tree. Our experiments have pointed strikingly to the tendency that the higher the temperature the more uniform is the distribution in all parts of the tree. As the temperature decreases the divergence in results increases between the top and bottom of the tree, in case of the liquid in favor of the bottom and in case of the pot in favor of the top of the tree. In the pot or portable generator the actual gas is produced more or less regardless of the atmospheric temperature, since the different chemicals when brought in contact will act upon one another to gen- erate the gas, during which action heat is also produced, and the warm gas readily rises. With the liquid vaporization must first occur, and low temperature, as well as high humidity, tends to retard such action. Moreover, when the gas is actually formed it is a cold gas and has a smaller tendency to rise in the tent. The atomizing of the liquid is in itself a cooling process. The bulb of a thermometer when held for a few moments before the nozzles as liquid hydrocyanic acid was being atomized showed a drop in temperature from 70° F to —4° F. The following table gives the total average '^kill" of ladybird beetles in the form "frees"^^ for the 1918 series of tests, which ex- tended over four months and included the use of about 25,000 insects. Bottom and center Top and center of tent of tent Pot 85.7% killed 91.1% killed Liquid 83.8% killed 76.9% killed 12 The form 'Hrees" consisted of a framework of wood in the shape of an ordinary citrus tree over which were placed ordinary fumigation tents. The dimensions were 26 X ^1> thus representing fair sized trees. 404 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION From the above it will be noted that the discrepancy in efficiency with the liquid occurs in the upper half of the tree. But the experi- ments also showed that this discrepancy was greatly reduced with the higher temperatures. Another tendency that has been indicated is: that a long exposure increases the effect of the gas from the liquid. This may be due to the slower diffusion, as well as the cooler gas from the liquid actually escaping more slowly through the tent. By the other methods of fumigation it is quite well established that there is no value in increasing the time of exposure beyond about forty-five minutes. As to whether the tendency of the gas from the liquid to remain largely in the lower half of the tree during low temperatures is a serious objection to its practical use, or whether it is practicable to increase the exposure, remains for further experience to determine. Heating the gas, or a better system of atomizing, or gasifying the liquid, are two possible ways of overcoming the poor diffusion, although this might complicate the field manipulations. THE EFFICIENCY OF LIQUID HYDROCYANIC ACID AS COMPARED WITH POT AND MACHINE GENERATION The killing efficiency of the liquid as compared with other methods of fumigation was determined: {a) by comparative tests in a fuma- torium; (&) by comparative tests under form trees; (c) by compar- ative tests in the field; and {d) by examination of commercial work in the field. In addition to the scale insects of citrus trees, for which pests fumigation work is carried on, ladybird beetles were used as an index of the results. Our two seasons' work with the beetles lead us to conclude that they are more desirable than scale insects as furnishing a sharp index of comparative fumigation results. In the case of scale insects, there may be 100 per cent killed with ordinary dosages, where these dosages vary as much as 25 per cent. With the highest dosage that may be used with safety to the citrus trees, some of the beetles will survive, and increasing numbers will survive as the dose is de- creased. It is possible also to determine the difference in results be- tween the top and bottom of a tree, with the beetles properly placed, while with the scale insects occurring naturally on the tree it is more difficult to make such a distinction. All of our results, however, are based on work both with the beetles and the scale insects. During the season of 1917, in our tests both in the field and under form trees, the results with the liquid were less satisfactory than the results carried on at the same time with the pot and cyanofumer. FUMIGATION WITH LIQUID HYDROCYANIC ACID 405 This may be accounted for from the fact that during that season the liquid was not of high purity until late in the season, and also because the machine in use that year was graduated on the recovery of only 12% gallons of liquid from a case of cyanide. In our examination of commercial fumigation, however, there was little if any difference that could be determined by the results on the scales in the field. During the season of 1918 our own tests again showed that the liquid was slightly less efficient than the pot method, although there was a marked improvement over the preceding year. In the field, as in 1917, no appreciable difference could be distinguished. Tests carried on with the cyanofumer and liquid on alternate trees in the same tent-throw, thus insuring similar conditions, failed to distinguish any difference either on beetles which were placed in the tree or on the scales on the fruit and foliage. The results thus determined, however, represent the effect on the insects within six or eight feet of the ground, which fact is important as discussed under the head of "Diffusion of the Gas." In our experiments with form "trees" the difference between the pot and liquid methods was brought out by considering the effect of the gas at three different points, namely, one foot from the top, one foot from the bottom, and in the center of the tree. When the results in the lower half only were considered, there was no important dif- ference between the pot and liquid methods. But when the results on the upper part of the tree were included, they were more favorable to the pot method. While, so far as field conditions and examination go within seven or eight feet of the ground, between the liquid and the older methods of fumigation the results have shown little important difference, we believe that a greater recovery of liquid from a given amount of cyanide is necessary, and that it is desirable to increase the amount given to the tree over that of the past two years. Judging from the field work, we had come to believe that when temperature conditions are favorable the gas from the liquid must be 10 to 15 per cent more effective than the same amount of gas from the pot or portable gen- erator. Fourteen gallons of liquid hydrocyanic acid of 96 or 98 per cent purity recovered from 200 pounds of sodium cyanide represent only 75 per cent of the total available gas, while by the other methods 90 per cent of the total gas in 200 pounds was recovered, making a difference of 15 per cent. Yet, during the past year, the 14 gallons of liquid was made to cover the same ground as 200 pounds of sodium cyanide generated by the other methods. When the results in all parts of the tree are considered, however, as shown by our 406 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION comparative tests for two seasons, we believe that, under normal con- ditions, practically the equivalent in the actual amount of gas must be used to effect the same results regardless of whether the source of the gas is from liquid hydrocyanic acid or from the pot or portable generator. Consequently 90 per cent at least, representing 17 gallons or 100 pounds of liquid hydrocyanic of 96 or 97 per cent purity, should be recovered from 200 pounds of sodium cyanide, and this amount should be made to cover the same ground as 200 pounds of sodium cyanide on the basis of the dosage schedules now in use. This would be equivalent to using approximately 20 cubic centimeters to correspond to one ounce of sodium cyanide (51-52 per cent cyanogen). (See discussion under ^'Graduation and Operation of Atomizing Machines," p. 398 and table 1, p. 412.) SUMMARY AND CONCLUSIONS Liquid hydrocyanic acid, a new means of citrus fumigation, first used on a commercial basis in 1917, has rapidly come into favor. The place where the greatest concentration of gas occurs under the tent from the liquid is practically the reverse of that from the pot or portable generator. "With the former method the most effective killing is at the bottom of the tree, while with the latter the most effective killing is at the top. Aside from the scale insects, more than 75,000 ladybird beetles have been used in our comparative tests as an index of results. The use of these insects has given discriminating data concerning the diffusion of gas under the tent, as well as on the efficiency of the different methods of fumigation, and these data have been verified by extensive field tests. The greatest possible yield is 108 pounds or 18.56 gallons of an- hydrous liquid hydrocyanic acid from 200 pounds of sodium cyanide (51-52 per cent cyanogen). The amount of liquid hydrocyanic acid (95-98 per cent) that has been recovered at the plant during the past year has been about 78 per cent of the total available. The amount of gas evolved by the pot or portable generator is estimated at 90 per cent of the total available gas. During the past year 75 per cent of the gas from a given amount of cyanide in the liquid form was made to cover the same ground as 90 per cent from the same amount by the ordinary methods of generation. FUMIGATION WITH LIQUID HYDROCYANIC ACID 407 Thus, while there has been a discrepancy of 10 or 15 per cent in the actual amount of gas used through the liquid method, the results in the field have not indicated any important difference on the scale insects. Our own tests, however, both in the field and laboratory, have indicated about such difference as would be expected. This apparent discrepancy between our own tests and commercial work in the field may be accounted for through the great variability in field work and by the difference, as has been determined, in the diffusion of the gas from the different methods. Field examinations are usually limited to an examination of the scales within six or eight feet of the ground. Our own tests have included the top of the tree as well. From these tests, when the results at the center and the bottom only were considered, there was practically no difference between the liquid and the pot, which harmonizes with the results in the field. When the results at the center and top only were considered, the pot method was more efficient than the liquid method. When the results in all parts of the tree are considered, it is necessary to use about 20 cubic centimeters of liquid hydrocyanic acid (96 or 98 per cent) to equal one ounce of sodium cyanide as given in the schedules of dosage now in practical use. Units representing 20 cubic centimeters may therefore be sub- stituted for the ounces, and the atomizing machines should be gradu- ated to deliver 20 cubic centimeters for each ounce called for in the schedules. II. PHYSICAL AND CHEMICAL PROPERTIES OF LIQUID HYDROCYANIC ACID By GEO. P. GRAY and E. R. HULBIRTi The ready acceptance of liquid hydrocyanic acid hy fumigators during the first year of its commercial production strongly empha- sized the need of a better knowledge of the physical and chemical properties of a liquid of such unusual characteristics. The Fruit Growers' Supply Company, the purchasing organization of the •California Fruit Growers' Exchange, were much concerned over the scarcity of information regarding the liquid being marketed, and financed an investigation of the plant and product of the Owl Fumi- gating Company at Azusa, California, during the month of August, 1918. This preliminary investigation not only proved to be of much value to the growers but also disclosed such a variety of questions to be answered that a co-operative arrangement for the continuation of the investigation was made between the supply company and this laboratory. The following pages constitute a report of these investi- gations. - COMMERCIAL CONSIDERATIONS The questions of most immediate concern appeared to be of a commercial nature. The liquid being delivered to consumers was not sold outright, but was delivered upon an exchange basis. The fumi- gators purchased their own sodium cyanide and brought it to the plant 1 Co-operating chemist, representing the Fruit Growers ' Supply Company. 2 The writers wish to express their appreciation of the attitude of Messrs. Ervin and WilHam Dingle, who have extended to them every courtesy during the course of the investigation and have given them the freedom of their plant, and have done everything in their power to facilitate the work. The Board of Trustees and Professor F. S. Hayden, Principal of the Citrus Union High School, have generously allowed the free use of their laboratories and apparatus. This accommodation has greatly facilitated the investigation by allowing the testing laboratory and the liquifying plant to be located in close proximity. The interest shown by Mr. R. S. Woglum and Mr. H. D. Young of the United States Bureau of Entomology in developing methods of analysis and in the test runs of the plant has been of great assistance. Mr. F. W. Braun, Mr. M. B. Pattison, and Mr. J. D. Neuls of the Braun Corporation have offered many suggestions, jjarticularly concerning methods of analysis. The many accommodations and courtesies extended by Mr. C. C. Hillis, Mr. C. A. Savage, and other officials of the Azusa-Covina-Gleudora Fruit Exchange are much appreciated. PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 409 for treatment. The plant furnished the sulfuric acid, generated, and liquefied the hydrocyanic acid at a fixed charge per case of sodium C3^anide. There appeared to be no well established idea as to what quantity of liquid should be recovered from a case of sodium cyanide under the operating conditions of the plant, though it was generally conceded that the quality of the liquid being delivered to the consumer was of good grade. Test Buns. — In order to determine the amount and quality of liquid recovered from a case of sodium cyanide under the operating conditions of the plant, the owners offered to make a test run to be carried on under the supervision of a representative of the Fruit Growers' Supply Company. The results of these tests were to be used as a basis of settlement between fumigator and plant. In order that the results should be above criticism of partiality, the following gentlemen kindly accepted an invitation to be present to witness the test run : Messrs. R. S. Woglum, entomologist, and H. D. Young, chemist, representing the U. S. Bureau of Entomology ; Professor H. J. Quayle, entomologist, representing the Citrus Experiment Station of the Uni- versity of California ; Mr. W. C. Bass, chemist, representing the Owl Fumigating Company ; and the senior writer, representing the Fruit Growers' Supply Company, and unofficially the Insecticide and Fungi- cide Laboratory of the University of California. The proposed pro- cedure of the test was outlined and agreed upon by the representatives present as being a fair one. Seventeen cases of sodium cyanide (3400 pounds) were weighed out and sampled for the test run. The plant was operated in the usual manner and the yield of liquid was weighed and sampled. The samples noted above were independently analyzed by Messrs. Young, Bass, and Gray. On comparing the results of analysis it was found that the three sets of results were in essential agreement. Not being willing to base conclusions upon a single run of the plant, another test was made a week later in a similar manner. The liquid hydrocyanic acid recovered in the first test run was 80.1 per cent of the greatest possible yield; in the second, 76.3 per cent ; an average of 78.2 per cent. The average purity of the liquid obtained in the first run was 97.57 per cent ; in the second, 94.27 per cent. While the yield of 78 per cent was quite disappointing, it must be recognized that this is an infant industry, and that with increasing knowledge and experience with the liquid continual improvement in all phases of its manufacture and use may be expected. The con- structors of the plant had no previous work to guide them in selection of their equipment. There were certain evident losses in the operation 410 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION of the plant which will doubtless be remedied before next season. It also appears that there are certain other losses, the causes of which are somewhat obscure. Quality of Liquid. — Frequent analyses and tests have been made of the liquid being delivered to consumers, covering a period from the first of August to the close of the fumigating season. The average purity of the liquid delivered to consumers has been above 95 per cent absolute hydrocyanic acid. Occasional drums of liquid have been noted which were considerably below this figure. After the plant was supplied with hydrometers so that the purity of the output could be quickly approximated, the delivery of a low-grade drum of liquid was rare. Liquid testing considerably below 95 per cent was returned to the crude liquid storage tank and redistilled. The writers are as yet undecided as to the comparative merits of a liquid testing, say, 95 per cent and one testing, say, 98 per cent or more. It is even maintained by some fumigators that the high per- centage of liquid is too volatile for safe handling, and that they much prefer a liquid testing 95 to 96 per cent. The definite determination of this point must be made by future investigation. In the present state of our knowledge, it is believed that a material testing 95 per cent or more of hydrocyanic acid is of a satisfactory grade. The plant as operating at present is quite capable of and does produce liquid of this quality, or better, many samples testing over 98 per cent. Return Per Case. — As the plant was operated during the past season and based upon the investigation reported above, the following is believed to be a fair return per case of two hundred pounds of sodium cyanide, testing 96-98 per cent of sodium cyanide : 1. A minimum of 85 pounds of absolute hydrocyanic acid ; or 2. A minimum of 90 pounds of liquid testing not less than 95 per cent hydrocyanic acid. Liquid of 95 per cent purity should not test less than 66° on the Baume hydrometer at a temperature of 60° Fahrenheit, corresponding to a specific gravity of .715. A gallon of liquid of this density would weigh 5.956 pounds. The above must not be taken as final. As the necessary infor- mation is accumulated it is confidently anticipated that the yield in the future will be equal to or even greater than that now obtained from the portable generators in common use. . Weight Basis. — Settlements are now made on a basis of gallons of liquid returned per case of sodium cyanide delivered. The liquid can be fairly easily measured when delivered to the consumer by an automatic measuring device, but measuring of so volatile and poisonous PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 411 a liquid without such a device is a rather dangerous undertaking and is not so easily subject to accuracy as weighing. It is strongly urged that the weight basis be adopted in transactions dealing with liquid hydrocyanic acid. The strongest argument in its favor is that the consumer would have a ready and convenient means of checking up deliveries. The weight of the empty drum could be determined and the figures painted on the drum. The weighing of the full drum only requires a short time, and in that way the weight of the liquid delivered would be determined by deducting the weight of the con- tainer from the gross weight. An additional argument in favor of the adoption of the weight basis in commercial transactions is evident from the following: The weight of the recovered liquid will be the same at any temperature. The corresponding number of gallons, however, will vary according to the temperature of the liquid. It has been held by some that the weight basis would place the consumer at a disadvantage for the reason that a low-grade liquid weighs considerably more than a high grade. It is not to be expected that a commercial product could be absolutely uniform. If, however, 95, 96, or some other percentage were finally adopted as the minimum standard of purity, the consumer would be justified in refusing any material of less purity than this. Fortunately it is unnecessary to have a chemical analysis made to determine purity. This can be determined accurately by observing specific gravity and temperature and using the appended reference tables. Table I following will be of use in making settlements for the return of liquid, in making dosage calculations, etc. The figures in the table showing yield in gallons are correct when the liquid is measured at a temperature of 15° C (60° F) only. 412 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION pq en o Eh O I— I o Ph W o o 1^ o o O <^ o o o o I— I w o o &< o o < o o m o o o o ^5 w o o o W ^ ^ t3 o M E-i M i-H O l-H M <! O ^ 5 EH ci:i «H • J3 o 'Cj > pi c3 pi • rH OJ 1— ( (V fH ,^ pi be HJ pq bX) ■^ fl rf) rt • r-l o ?3 P 0) •rs ^ ^ fl Ci ^H c3 I— 1 o c^ o <11 •l-H rd ^ Q PI Q O 4^3 O • l-< s > ^ fl c3 bx) d 05 ^ ^ Ph o C/J ^ ^ o o Pi S ;=! ^ o d ^ ^S -^ ""^ f's ■^ ^ b. PI — I hH O M 03 d rd ® be PS OS ^ ^ H Pl o CO 03 d 4 ^ ^ CO o .2 CO CO GO fc-l f eg be 00 'Fi CO ^ ^- ^ O CO o 00 O) 00 o u a;* o 3 o o O 73 1^ ^ 05 o o O) 73 03 -< ^H o m Pl .O *C 73 ,be -M ^' o fe W) M S ?^ 41 . OOOiO 1— ii— i(M CO"^»OCOI>- cc ... ... ..... fcCi— 1»— I,— I ,_<,_|,_, ,_i,_(,_|,_|,_H l-H ■^COt-i 0005 Oi0505050 ^i:Ot^G0 OiOO T-HC^cOTtHCO i=:QOO0O0 00O1O5 Oi Oi Oi Oi C:> . OOCOIO cocoes CO(M(NCOCO ^l>.O0Oi Ot-I(M COTtiiOcOl>- 6X)iO>OK5 cOcDCO COCOCOCDCO rHf— It— 1 rH,— I,— ( i— IrHi— IrHi— I 001>1>. CDcOcO I>I>00050 MT-IC^CO -^lOcO t^00OiC(M -Q OiOiCi 05050i 05010500 . rH,— 105 oor^oo ooooooOi— I i2J>0000 CiOi— I <MC0rtlCOt> cS ... ... (M(M(M <M(MCO -^lOCOOOO «!j>00Oi O,— iC<l COrj^iOCDOO £ 05050i ooo ooooo •.CO(NCO COWCO CO»OCD1:^0 ^COt^OO CJlOrH C<1CO"<*»OI> c3 • • • • • . ..... t>Cl>l>J> I>OCOO 0000000000 COCOI:^ OOOiO ,-iCOiOI>0 5 ooo ooo O'—''— ''—''— I ZD <:D zC zo OO t^ O'— 'C^^OO oJiOCOt^ OOOIO (MCO-^OCO yjoooooo ooooai ojosoiOiOi Ot— l<M fOiOCO 05'— icot^o S'oOOiO i-i(MCC TlHCDt^OOO SOOi— I tH,— I,— I rHl— ti— li— IC^ OOiOCO 1— (OOCD T:tH(NO00l:^ . ,— i-^t^ 0(NiO OOi— 1'*<^0 2 000000 Oi Oi Oi OiOOOO ^ ... ... r o O 05 00 O 05 05 t^ '-O lO 05 Oi Oi 'tH CO (M "-H O Oi CI Oi Oi Oi >,>,>. t^ t~i t- <u o o o tS -h3 H-3 -t-i 03 OOO U d d d rh e+H t)-H <4-H -a -i:; ^ M cc tn bC bC hC -M H-i -M WWW o3 o3 1^ mm m ^ ^ ^ ^ ^ ooooo H^l ^ H^ H^ h^ PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 413 PHYSICAL PROPERTIES Miscibility. — During the earlier stages of the commercial produc- tion of the liquid it was erroneously believed that mixtures of hydro- cyanic acid and water would separate on standing into layers of different composition. The reason for this belief was that the first run in the morning was often diluted with water remaining in the condensors and conveying pipes after flushing at the end of the previous day's run. As soon as this point was established it became the custom at the plant to draw off the first run of low-grade liquid and return it to the crude liquid receiver to be redistilled. It has been determined that hydrocyanic acid is miscible with water in all proportions. When once thoroughly mixed, the liquid remains homogeneous throughout, except as affected by chemical de- composition. When the two are mixed there is always an appreciable contraction in volume accompanied by a fall in temperature. This fact complicated the problem of determining the relation of percentage purity to specific gravity and necessitated extensive experimentation, as will be described under a later heading. Evaporation. — The anhydrous liquid has a very strong affinity for water, so if a high-grade liquid is exposed to moist air it will either absorb moisture from the air and become dilute or, the acid being more volatile than water, will evaporate at a greater rate, leaving a residue of low-grade liquid. A cylinder was filled with a much diluted and thoroughly mixed sample of hydrocyanic acid. This was analyzed and then the cylindei' was allowed to stand uncovered in an exposed place for fifteen hours, so that evaporation might proceed readily. In that time about 30 per cent of the liquid had evaporated. A sample of the remaining liquid was then analyzed, and the results were as follows: Sample from cylinder at first: 46.6% hydrocyanic acid. Sample from cylinder after evaporation: 29.4% hydrocyanic acid. A high-grade liquid evaporates so rapidly that its temperature is lowered at times even to the point where particles of ice are formed. In experimenting with the liquid in a room where the temperature was about 90° F, and in a good current of air, a cylinder was filled with the liquid and enough more added so as to run down the sides of the cylinder. The temperature of the liquid was reduced ten degrees in ten minutes. This is a very desirable property, for if the liquid is warmed up to near the boiling point and allowed to evaporate freely it is automatically cooled and evaporation thus retarded. 414 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Vapor pressure has an important bearing on the strength of materials required for containers. Apparently the vapor pressure of hydrocyanic acid is very small. In other words, a comparatively slight pressure is required to retain the substance in a liquid state, even at temperatures near its boiling point. The writers have as yet been unable to investigate this matter, but the figures shown in Table II are contributed through the courtesy of Mr. W. C. Bass of Los Angeles as being approximately correct. TABLE II Pressure of Hydrocyanic Acid (About 97% HCN) in a Closed Container at Different Temperatures Temp. deg. F Pounds pe 87 3.4 94 4.9 100 7.9 105 9.8 110 11.8 115 13.3 120 15.7 125 17.7 SPECIFIC GRAVITY It is important for the fumigator to know the approximate per- centage of hydrocyanic acid in the liquid which he uses in order to enable him to reject material of low grade. This is of special im- portance if the weight basis be adopted in making settlement. The sampling and analyzing of a poisonous and volatile material of this sort presents unusual difficulties. Inasmuch as the density of the pure liquid is less than three-fourths that of water and the principal impurities which are apt to be encountered in a commercial liquid are water or other impurities which are heavier than the pure liquid, it was early recognized that the determination of specific gravity might be utilized in approximating the percentage purity of a com- mercial liquid. This view was confirmed by preliminary experiments and a hydrometer spindle has been used throughout the course of these investigations as a ready and satisfactory means of approxi- mating purity of the output of the plant. The specific gravity of the liquid materially changes with varying temperatures. Also on account of the contraction in volume when PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 415 water and acid are mixed the rate of variation varies according to the percentage of water and acid in the sample. These complications, however, do not interfere with the application of this method of approximation, provided the extent of these variations are known. This matter was gone into very thoroughly and data have been obtained giving complete information on all of the points involved. These data, presented in the reference tables at the end of this bulletin, were determined by means of a hydrometer spindle accurate to the third decimal place. The temperature was observed in degrees of the Centigrade scale. Table VI will indicate the percentage of absolute hydrocyanic acid corresponding to various densities and at a range of temperature from 5° to 22° C. Hydrometer spindles graduated in specific gravity are not as readily obtainable as spindles reading in degrees Baume. In order to make the tables available for use with a Baume hydrometer, they have all been recalculated, indicating the corresponding Baume reading and the variation in temperature according to the Fahrenheit thermometer. These data are given in Table VII. These determinations were all made upon the commercial liquid. The specific gravity at different temperatures of 100 per cent material, however, has been calculated from the data for liquids of lower per- centages. It is interesting to note that the calculated specific gravity at 18° C of 100 per cent acid is .6943. The commonly accepted specific gravity of this material is .6967.^ The close agreement of these two figures is believed to be a confirmation of the accuracy of the determinations. Thirteen samples of liquid hydrocyanic acid were selected, being representative samples of the product of the liquefying plant over a period of three months. Some were intentionally diluted with water. The temperature of the samples was made to vary and conditions so arranged that they would afford a fair measure of the accuracy of the tables. The specific gravity and temperature of each were care- fully observed and the percentage of hydrocyanic acid determined by reference to the tables, and then by careful analysis. The results are shown in Table III. The laboratory analysis is accurate to two- tents of 1 per cent. Since there is no greater variation than the experimental error between the percentages determined by analysis and by the tables and since the conditions of the samples were made quite variable, the following table is considered to be a positive justi- fication of the tables and confirmation of their accuracy. 3 H. E. Williams, Chemistry of Cyanogen Compounds, and their Manufacture and Estimation. J. and A. Churchill, London, 1915. Observed specific gravity Temperature deg. C .736 17 .7115 16 .704 16.5 .7045 16 .705 16 .704 16 .715 16.5 .716 16 .720 5.25 .713 10 .7405 13.5 .742 12 .7185 14 HCN by tables % 88.2 95.6 97.7 97.8 97.7 97.9 94.5 94.4 97.7 97.7 88.1 88.2 94.5 416 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION TABLE III Comparison of Eesults Obtained on Determination of HCN by Using Our Eeference Tables and by Analysis HCN by analysis % 88.2 95.6 97.8 97.9 97.7 98.1 94.7 94.6 97.7 97.7 88.2 88.2 94.7 Use of the Tables. — The tables referred to above make it possible to determine the quality of the liquid in a moment's time by the use of a hydrometer spindle graduated either in specific gravity or Baume degrees, taking into account the temperature of the liquid. Many of these spindles are provided with a thermometer, so that both observations can be made from one instrument. It requires no tech- nical skill to make such observations. Any one w^ithout previous experience can easily read the hydrometer accurately v^^ithin one degree Baume. This introduces an error of approximately 1 per cent. With a little practice and with an accurately graduated instrument an even closer approximation than this can be made. After the hydrometer reading and the temperature of the liquid have been taken, the corresponding percentage is determined by referring to Table VI if the spindle reads in specific gravity or to Table VII if the Baume hydrometer has been used. The Cyanometer. — The accumulation of the data referred to above has made possible the construction of a hydrometer graduated directly in percentage hydrocyanic acid. The idea of such an instrument is not a new one. In fact, alcoholometers, salometers, saccharometers, etc., are in common factory use for the determination of alcohol in mixtures of alcohol and water, salt in brine, and sugar in syrup respectively. Our data have made possible the construction of a ''cyanometer" to be used for a purpose similar to the above. It is possible that the somewhat restricted use for these instruments might not make their construction attractive to instrument makers. In this case the reference tables are available. If, however, the idea appeals PHYSICAL AND CHEMICAL PROPERTIES OP HYDROCYANIC ACID 417 to the fumigators as of sufficient importance and the demand is great enough, an instrument could be procured which will indicate per- centages of hydrocyanic acid directly. This, of course, should be provided with a thermometer and with a table of temperature cor- rections. All of these data could easily be contained within the glass shell of the average hydrometer. A simplified scale for the graduation of this instrument as well as a table for temperature correction is shown below. TABLE IV Data for Construction of the Cyanometer Marked on scale Corresponding marks on hydrometers Temperatu re corrections HCN% ateO^F Baume reading at 60° F Specific gravity equivalent to Baume A deg. P Corections 100 71.0 .697 70 -2% 99 69.8 .701 65 -1% 98 68.7 .705 60 97 67.8 .708 55 + 1% 96 66.9 .711 50 +2% 95 65.9 .715 45 +3% 94 65.0 .718 40 +4% 93 64.1 .72] 92 63.2 .725 91 62.3 .728 90 61.4 .732 89 60.6 .735 88 59.7 .738 87 58.8 .742 86 58.0 .745 85 57.1 .748 An instrument of this kind is commonly calibrated for use at a temperature of 60° F, and is correct at that temperature only. If used at any other temperature than the above the observed reading should be corrected according to the variation above or below the temperature at which the instrument is calibrated. CHEMICAL PROPERTIES Hydrocyanic Acid; Priissic Acid Chemical Symbol, HON; Molecular Weight, 27.02 DECOMPOSITION Most impurities tend to accelerate the decomposition of hydro- cyanic acid. The purer the liquid is the better its keeping qualities. Impurities may be present especially from contact with metals or in 418 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION the form of other products. These may have their origin in the manu- facturing plant or in the containers used for handling and dispensing the liquid. Some metals react with the liquid and the metallic cyan- ides thus formed may later be precipitated, forming a troublesome sediment. In some cases they can be easily removed by straining. Some of the causes of decomposition are solely under the control of the manufacturer, while others are under the control of the fumigator. "When the liquid decomposes it forms several substances which themselves accelerate decomposition of fresh liquid with which they come in contact. In other words, decomposition appears to be a cumulative process. Undesirable impurities may be imperceptible in a freshly prepared liquid, but nevertheless have their effect. The decomposition is gradual at first and is marked with the appearance of a faint yellow tint and an accompanying lowering of percentage of hydrocyanic acid. As this proceeds the color becomes deeper and merges into brown, when the chemical changes take place more rapidly and new gases are formed in great quantity. At this stage a dark brown or black flaky precipitate is formed. After complete decom- position the newly formed gases have escaped, leaving a bulky, black sediment much resembling carbon, or, if the liquid is confined, the pressure of these gases is oftentimes sufficient to burst the container. The above description is well illustrated by the following record of a decomposed sample. Table V. TABLE V Record of a Decomposed Sample % HON 94.7 93.8 93.2 93.2 93.3 92.8 92.3 92.3 90.2 80.0 Warning Signs. — So far as observed, when a sample starts to de- teriorate a color of some sort, usually yellow, is always formed. Am- monia seems to be one of the gases formed in greatest quantity, or at least one which can most readily be detected in decomposing hydro- cyanic acid. The formation of any color or an odor of ammonia then may be taken as a warning. Analysis Date, 1918 Color of sample Weather 1 Oct. Straw color warm 2 4 Amber warm 3 8 Amber warm 4 14 Amber cool 5 16 Amber cool 6 21 Yellow cool 7 25 Yellower cool 8 29 Very yellow • • cool 9 ^ ov. 2 Brownish yellow warm 10 4 Black sludge cool PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 419 Keeping Qualities. — The question has often been asked, how long the liquid will keep. This question cannot be answered easily. Some samples several years old are apparently as good now as when first prepared. Other samples decomposed completely within a few days or weeks. One apparently good sample which was closely observed completely decomposed in forty days. Another sample of similar ap- pearance and kept under the same conditions was as good at the end of four months as it was at first. The natural life of the liquid de- pends upon its history in the course of manufacture as well as upon conditions of handling and storage. Some of the factors influ- encing the keeping qualities of the liquid are discussed below. Dilution. — Our experiments point toward the conclusion that the presence of water, especially in amounts more than 5 per cent, are favorable to decomposition and tend to increase the effect of the acid upon many metals. It is probable that a liquid as nearly anhydrous as could be produced would be the most desirable from these stand- points. The great volatility of a liquid of this nature, however, may necessitate a compromise between the highest purity obtainable and one more convenient to handle. Temperature. — The liquid resists decomposition much better at low temperatures, other conditions being the same, than it does at high temperatures. If held in an open container it would boil at a tem- perature of about 80° F. The liquid should be kept cool at all tinies, preferably never becoming warmer than 60° F. If the liquid is allowed to become sufficiently warm, it is very easy to see that a closed drum of liquid could be burst (see Table II). Some of the explosions of previous years may be partly accounted for from this cause, as well as from the decomposition of the liquid producing gases of greater vapor pressure than hydrocyanic acid. Decomposition Residue. — The dark colored deposit from a partly decomposed sample has been demonstrated to be highly favorable to decomposition when placed in a fresh sample. This matter has an important bearing on the washing out of delivery containers, atomizing machinery and any other vessels used in storage or handling. Invest- igations are under way in an effort to disclose some substance which can be used to change the nature of this deposit so that it would not be so favorable to decomposition. Sufficient progress has not been made to warrant publication. A portion of the black solid residue remaining after a sample of hydrocyanic acid had completely decomposed was spread out and left exposed to the air for three weeks. At the end of that time some of this solid, resembling charcoal in appearance, was added to some hydro- 420 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION cyanic acid in a small flask and set away. The liquid became slightly yellow as soon as the material had settled. Within one day the liquid was brownish yellow ; in four days, brown and throwing down a de- posit ; within two weeks, the liquid had completely decomposed. The same lot of liquid without the addition of decomposition residue remained unimpaired for several months. Some of the black deposit being thrown down from a decomposing sample was filtered from the liquid and added to a fresh portion of clear liquid and then set away. The effect was in all respects the same as described above, except that the chemical action was consid- erably slower. In four days the liquid had become bright lemon yellow ; in two weeks, brown ; and in five weeks had completely de- composed. Alkalies. — It has been long known that alkalies are favorable to decomposition. This has been confirmed in our investigations using sodium, potassium, and ammonium hydroxides. Ammonia was found to be the most energetic. Acids. — Sulfuric acid and hydrochloric acid even when used in large amounts do not appear to affect the liquid seriously. Nitric acid, however, has a very serious influence. Sodium Cyanide. — The undesirable effect of sodium cyanide is equal to or even greater than the alkalies mentioned above. Soap. — Several varieties of soap were found to decompose the liquid very rapidly. Doubtless this is due to the presence of alkali or to hydrolysis of alkali salts. Packing Materials. — Quite a variety of the more common packing materials — pure rubber, red rubber, white rubber, leather, "garlock", an asbestos packing, and an asphalt canvas packing — were experi- mented with. So far as we were able to observe, there is nothing dangerous about any of these ordinary materials used for packing so far as the decomposing effect on hydrocyanic acid is concerned. Rubber does not appear to affect the liquid, but the rubber itself is sooner or later destroyed. Metals. — Some metals are attacked by the acid. On the other hand, some metals seem to act as catalytic agents and promote a rapid decomposition of the acid. Others apparently have no effect what- ever. The metals appearing to act upon the acid more energetically are : lead, com,mercial tin, solder, cast iron, and steel. These metals very clearly should be avoided in the construction of liquefying plants and in delivery containers, atomizing machinery, fittings, etc. PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 421 ACTION ON METALS A series of experiments was made to test the action of liquid hydrocyanic acid on various metals, the object being to obtain data for the intelligent selection of materials for the construction of de- livery containers, atomizing apparatus, condensers and other equip- ment for use in connection with the new industry. Small pieces of various metals, solid and plated, were first weighed and then sealed in glass tubes containing a small quantity of liquid hydrocyanic acid. The amount of liquid was regulated so that only a part of the metals was exposed to the liquid while the remainder was exposed to the vapors. These specimens have been under obser- vation for four months and would all have furnished fairly complete data on the action of the acid on the commoner metallic substances except for the recent suspicion that the glass itself may have been responsible for the decomposition of the liquid. Our experiments have shown that certain kinds of glass under some conditions appear to cause the decomposition of liquid hydro- cyanic acid. So far as we are able to determine, boro-silicate glass does not affect the liquid. The experiments are therefore being re- peated, using this kind of glassware for the test containers. A large variety of metals and various enamels and varnishes are also being tested. The complete results of these experiments, however, will not be available for the coming fumigating season. Resistant Metals. — Notwithstanding the possible combined influence of metal and glass upon liquid hydrocyanic acid, a few metals have not been affected by four months' contact with prussic acid. Alumi- num, block tin, and pure zinc apparently are not changed in the least and the liquid in contact with them is as clear and colorless as when first sealed up. The liquid on the brass, nickel, and silver has become slightly yellow ; that on the copper is still good, but the copper has a somewhat roughened appearance as if it had been slightly acted upon. While pure zinc noted above is apparently quite resistant to the action of prussic acid, a piece of plumbers' ordinary sheet zinc was soon covered with a white coating and a considerable quantity of white sediment was deposited in the liquid. The liquid itself remained colorless and apparently unaffected throughout the experiment. Delivery Druyns. — Judging from the experiments described above and from a consideration of the cost and properties of the various materials observed, aluminum is the most promising material for the construction of delivery drums. Brass fittings appear to be per- missible. 422 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION SUMMARY The ready acceptance, by fumigators, of liquid hydrocyanic acid as a new convenience in citrus fumigation has resulted in a study of the physical and chemical properties of the liquid. Two test runs of the liquefying plant were made in order to estab- lish a basis of settlement between plant and fumigator. The liquid hydrocyanic acid recovered in the first test run was 80.1 per cent of the greatest possible yield ; in the second, 76.3 per cent ; an average of 78.2 per cent. The average purity of the liquid obtained in the first run was 97.57 per cent ; in the second, 94.27 per cent. The average purity of the liquid delivered during the past fumi- gating season w^as above 95 per cent absolute hydrocyanic acid. Material of 95 per cent or greater purity is considered of a satisfac- tory grade. As the plant was operated last season, the following is believed to be a fair return per case of two hundred pounds of sodium cyanide : 1. A minimum of 85 pounds of absolute hydrocyanic acid; or 2. A minimum of 90 pounds of liquid testing not less than 95 per cent purity. As the necessary information is accumulated it is confidently an- ticipated that the yield in tbe future will be equal to or even greater than that now obtained from the portable generators in common use. The weight basis for commercial transactions is strongly urged for adoption in preference to the volume basis now in use. Deliveries could be more easily checked up by weighing than by measuring, and this is also less dangerous. Furthermore, the weight of the recovered liquid will be the same at any temperature, while the corresponding number of gallons will vary according to the temperature at which it is measured. A table has been prepared showing the weights and corresponding volumes of various grades of commercial liquid and the quantities thereof corresponding to various percentages of the maximum yield (Table I). It has been determined that the acid is miscible with water in all proportions and will not stratify upon standing. Hydrocyanic acid evaporates more rapidly than water from dilute mixtures of the two. Complete data have been obtained on the specific gravity of com- mercial liquid hydrocyanic acid testing from 70 per cent to 100 per PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 423 cent purity, and upon the extent of variation of hydrometer readings as affected by temperature. These figures are presented in the form of reference tables at the end of the bulletin. These tables make it possible to determine the quality of a liquid in a moment's time by the use of a hydrometer graduated either in specific gravity or Baume degrees. The accumulation of the data referred to above has made possible the construction of a cyanometer, a hydrometer graduated directly in percentages of hydrocyanic acid and provided with a simple table of temperature corrections. A method of analysis has been selected and shown to give concord- ant results within two-tenths of 1 per cent. The development of any color, usually yellow, or an odor of am- monia may be taken as a warning of incipient decomposition of the liquid. Factors and materials favoring decomposition are : water in excess of 5 per cent ; high temperatures ; residue from a decomposed liquid ; all alkalies, nitric acid, sodium cyanide ; soap ; or contact with lead, commercial tin, impure zinc, solder, cast iron, or steel. The following metals were found to be highly resistant to the acid, somewhat in the order named : aluminum, block tin, pure zinc, brass, nickel, silver, and copper. Aluminum is the most promising material for the construction of delivery drums. Brass fittings are permissible. REFERENCE TABLES The following reference tables and their use in determining the percentage of absolute hydrocyanic acid in commercial liquid hydro- cyanic acid have been discussed under the heading ' ' Specific Gravity ' ' in the section on physical properties. 424 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE VI For Use With Specific Gravity Hydrometer Calibrated at 15° C Observed Temperature ° C Observed Specific 22 21 20 19 18 17 16 15 14 Gravity Corresponding Percent, l Hydrocy; anic Acid .690 99.7 .692 99.1 99.5 99.9 .694 98.5 98.9 99.3 99.7 .696 97.9 98.3 98.7 99.1 99.5 99.9 .698 97.3 97.7 98.1 98.5 98.9 99.3 99.7 100 .700 96.7 97.1 97.5 97.9 98.3 98.7 99.1 99.6 100 .702 96.1 96.5 96.9 97.3 97.7 98.1 98.5 98.9 99.4 .704 95.5 95.9 96.3 96.7 97.1 97.5 97.9 98.4 98.8 .706 94.9 95.3 95.7 96.1 96.5 96.9 97.3 97.8 98.2 .708 94.3 94.7 95.1 95.5 95.9 96.3 96.7 97.1 97.6 .710 93.7 94.1 94.5 94.9 95.3 95.7 96.1 96.5 97.0 .712 93.1 93.5 93.9 94.3 94.7 95.1 95.5 95.9 96.4 .714 92.6 93.0 93.4 93.8 94.2 94.6 95.0 95.3 95.8 .716 92.0 92.4 92.8 93.2 93.6 94.0 94.4 94.7 95.2 .718 91.4 91.8 92.2 92.6 93.0 93.4 93.8 94.1 94.6 .720 90.8 91.2 91.6 92.0 92.4 92.8 93.2 93.6 94.0 .722 90.2 90.6 91.0 91.4 91.8 92.2 92.6 93.0 93.4 .724 89.6 90.0 90.4 90.8 91.2 91.6 92.0 92.4 92.8 .726 89.0 89.4 89.8 90.2 90.6 91.0 91.4 91.8 92.2 .728 88.5 88.9 89.3 89.7 90.1 90.5 90.9 91.2 91.6 .730 87.9 88.3 88.7 89.1 89.5 89.9 90.3 90.6 91.0 .732 87.3 87.7 88.1 88.5 88.9 89.3 89.7 90.0 90.4 .734 86.7 87.1 87.5 87.9 88.3 88.7 89.1 89.4 89.8 .736 86.2 86.5 87.0 87.4 87.8 88.2 88.6 88.8 89.2 .738 85.6 86.0 86.4 86.8 87.2 87.5 87.9 88.2 88.6 .740 85.0 85.4 85.8 86.2 86.6 86.9 87.3 87.6 88.0 .742 84.4 84.8 85.2 85.6 86.0 86.3 86.7 87.0 87.4 .744 83.8 84.2 84.6 85.0 85.4 85.7 86.1 86.4 86.8 .746 83.3 83.7 84.1 84.5 84.8 85.1 85.5 85.8 86.2 .748 82.7 83.1 83.5 83.9 84.2 84.5 84.9 85.2 85.6 .750 82.1 82.5 82.9 83.3 83.6 83.9 84.3 84.6 85.0 . 752 81.6 82.0 82.4 82.7 83.0 83.3 83.6 84.0 84.4 .754 81.0 81.4 81.8 82.1 82.4 82.7 83.1 83.5 83.8 .756 80.4 80.8 81.2 81.5 81.8 82.1 82.5 82.9 83.2 PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 425 Observed Specific Gravity .690 .692 .694 .69) .698 .700 .702 .704 .706 .708 .710 .712 .714 .716 .718 .720 ,722 .724 726 .728 ,730 ,732 ,734 ,736 ,738 ,740 ,742 ,744 ,746 ,748 .750 ,752 .754 ,756 TABLE VI (Continued) For Use With Specific Gravity Hydrometer Calibrated at 15° C 13 12 Observed Temperature ° C 11 10 9 8 7 Corresponding Percent. Hydrocyanic Acid 6 99.8 ........ 99.2 99.6 100 98.6 99.0 99.4 99.8 98.0 98.4 98.8 99.2 99.6 100 97.4 97.8 98.2 98.6 99.0 99.4 99.9 96.8 97.2 97.6 98.0 98.4 98.8 99.3 99.7 96.2 96.6 97.0 97.4 97.8 98.2 98.7 99.1 99.6 95.6 96.0 96.4 96.7 97.2 97.6 98.1 98.5 99.0 95.0 95.4 95.8 96.1 96.6 97.0 97.5 97.9 98.4 94.4 94.8 95.2 95.5 96.0 96.4 96.9 97.3 97.8 93.8 94.2 94.5 94.9 95.3 95.8 96.2 96.6 97.1 93.2 93.6 93.9 94.3 94.7 95.1 95.6 96.0 96.5 92.6 93.0 93.3 93.7 94.1 94.5 95.0 95.4 95.9 92.0 92.4 92.8 93.1 93.5 93.9 94.3 94.7 95.3 91.4 91.8 92.2 92.5 92.9 93.3 93.7 94.1 94.7 90.8 91.2 91.6 91.9 92.3 92.7 93.1 93.5 94.0 90.2 90.6 91.0 91.3 91.7 92.1 92.5 92.9 93.4 89.6 90.0 90.4 90.7 91.1 91.5 91.9 92.3 92.8 89.0 89.4 89.8 90.1 90.5 90.9 91.3 91.7 92.2 88.4 88.8 89.2 89.5 89.9 90.3 90.7 91.1 91.6 87.8 88.2 88.6 88.9 89.3 89.7 90.1 90.5 91.0 87.2 87.6 88.0 88.3 88.7 89.1 89.5 89.9 90.4 86.6 87.0 87.4 87.7 88.1 88.5 88.9 89.3 89.8 86.0 86.4 86.8 87.1 87.5 87.9 88.3 88.7 89.1 85.4 85.8 86. 2 86.5 86.9 87.3 87.7 88.1 88.5 84.8 85.2 85.6 85.9 86.3 86.7 87.1 87.5 87.9 84.2 84.6 85.0 85.3 85.7 86.1 86.5 86.9 87.3 83.6 84.0 84.4 84.7 85.1 85.5 85.9 86.3 86.7 426 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE VII For Use With Baume Hydrometer Calibrated at 60°F. Observed Temperature °F. Observed Degrees 70 69 68 67 66 65 64 63 62 61 60 Baume. Corresponding Percent. ; Hydrocyanic Acid 72.5 99.7 100 72.0 99.1 99.3 99.5 99.7 99.9 71.5 98.6 98.8 99.0 99.2 99.4 99.7 100 71.0 98.1 98.3 98.6 98.8 99.0 99.2 99.4 99.6 99.8 100 , 70.5 97.6 97.8 98.0 98.2 98.4 98.6 98.8 99.1 99.3 99.5 99.7 70.0 97.1 97.3 97.5 97.7 98.0 98.2 98.4 98.7 98.9 99.1 99.3 69.5 96.6 96.8 97.0 97.2 97.4 97.6 97.8 98.0 98.2 98.4 98.7 69.0 96.1 96.3 96.5 96.7 97.0 97.2 97.4 07.6 97.8 98.1 98.3 68.5 95.5 95.7 95.9 96.1 96.4 96.6 96.9 97.1 97.3 97.6 97.8 68.0 95.0 95.2 95.4 95.6 95.9 96.1 96.3 96.5 96.8 97.0 97.2 67.5 94.4 94.6 94.8 95.0 95.3 95.5 95.7 95.9 96.1 96.4 96.6 67.0 93.9 94.1 94.3 94.5 94.8 95.0 95.2 95.4 95.6 95.9 96.1 66.5 93.4 93.6 93.8 94.0 94.3 94.5 94.7 94.9 95.2 95.4 95.6 66.0 92.9 93.1 93.3 93.5 93.7 94.0 94.2 94.4 94.6 94.9 95.1 65.5 92.4 92.6 92.8 93.0 93.2 93.5 93.7 93.9 94.1 94.3 94.5 65.0 91.8 92.0 92.2 92.4 92.6 92.8 93.1 93.3 93.5 93.7 93.9 64.5 91.2 91.4 91.6 91.8 92.1 92.3 92.5 92.7 92.9 93.2 93.4 64.0 90.7 90.9 91.1 91.3 91.6 91.8 92.0 92.2 92.4 92.7 92.9 63.5 90.1 90.3 90.5 90.7 90.9 91.2 91.4 91.6 91.8 92.1 92.3 63.0 89.6 89.8 90.0 90.2 90.5 90.7 90.9 91.1 91.4 91.6 91.8 62.5 89.1 89.3 89.5 89.7 89.9 90.2 90.4 90.6 90.8 91.0 91.2 62.0 88.5 88.7 88.9 89.1 89.3 89.6 89.8 90.0 90.2 90.4 90.6 61.5 88.0 88.2 88.4 88.6 88.8 89.0 89.3 89.5 89.7 89.9 90.1 61.0 87.3 87.5 87.7 87.9 88.1 88.3 88.6 88.8 89.0 89.2 89.4 60.5 86.8 87.0 87.2 87.4 87.6 87.8 88.0 88.3 88.5 88.7 88.9 60.0 86.3 86.5 86.7 86.9 87.1 87.4 87.6 87.8 88.0 88.2 88.4 59.5 85.8 86.0 86.2 86.4 86.6 86.8 87.0 87.2 87.4 87.6 87.8 59.0 85.2 85.4 85.6 85.8 86.0 86.2 86.4 86.6 86.8 87.0 87.2 58.5 84.6 84.8 85.0 85.2 85.4 85.6 85.8 86.0 86.2 86.4 86.6 58.0 84.0 84.2 84.4 84.6 84.8 85.0 85.2 85.4 85.6 85.8 86.0 57.5 83.5 83.7 83.9 84.1 84.3 84.5 84.7 84.9 85.1 85.3 85.5 57.0 82.9 83.1 83.3 83.5 83.7 83.9 84.1 84.3 84.5 84.7 84.9 56.0 82.3 82.5 82.7 82.9 83.1 83.3 83.5 83.7 83.9 84.1 84.3 PHYSICAL AND CHEMICAL PROPERTIES OF HYDROCYANIC ACID 427 TABLE VII (Continued) For Use With Baume Hydrometer Calibrated at 60°F. Observed Temperature °F. Observed Degrees 59 58 57 56 55 54 53 52 51 50 Baume Corresponding ; Percent. Hydrocyanic Acid 72.5 72.0 71.5 71.0 70.5 100 70.0 99.6 99.8 100 69.5 99.0 99.2 99.4 99.6 99.8 100 69.0 98.5 98.7 98.9 99.1 99.3 99.5 99.8 100 68.5 98.0 98.2 98.4 98.6 98.8 99.0 99.3 99.5 99.7 100 68.0 97.4 97.6 97.8 98.1 98.3 98.5 98.8 99.0 99.2 99.5 67.5 96.9 97.1 97.3 97.5 97.8 98.0 98.2 98.4 98.6 98.9 67.0 96.3 96.5 96.8 97.0 97.2 97.5 97.7 97.9 98.1 98.4 66.5 95.8 96.0 96.3 96.5 96.7 96.9 97.1 97.4 97.6 97.8 66.0 95.3 95.5 95.7 96.0 96.2 96.4 96.6 96.9 97.1 97.3 65.5 94.7 95.0 95.2 95.4 95.6 95.9 96.1 96.3 96.5 96.7 65.0 94.1 94.4 94.6 94.8 95.0 95.3 95.5 95.7 95.9 96.1 64.5 93.6 93.8 94.0 94.3 94.5 94.7 94.9 95.1 95.3 95.5 64.0 93.1 93.3 93.5 93.7 94.0 94.2 94.4 94.6 94.8 95.0 63.5 92.5 92.7 92.9 93.1 93.4 93.6 93.8 94.0 94.2 94.4 63.0 92.0 92.2 92.4 92.6 92.9 93.1 93.3 93.5 93.7 93.9 62.5 91.4 91.7 91.9 92.1 92.3 92.5 92.7 92.9 93.1 93.3 62.0 90.8 91.0 91.3 91.5 91.7 91.9 92.1 92.3 92.5 92.7 61.5 90.3 90.5 90.7 90.9 91.1 91.3 91.5 91.8 92.0 92.2 61.0 89.6 89.8 90.0 90.4 90.5 90.7 90.9 91.2 91.4 91.6 60.5 89.1 89.3 89.5 89.8 90.0 90.2 90.4 90.6 90.8 91.0 60.0 88.6 88.8 89.0 89.3 89.5 89.7 89.9 90.1 90.3 90.5 59.5 88.0 88.3 88.5 88.7 88.9 89.1 89.3 89.5 89.7 89.9 59.0 87.4 87.6 87.9 88.1 88.3 88.5 88.7 88.9 89.1 89.3 58.5 86.8 87.0 87.3 87.5 87.7 87.9 88.1 88.3 88.5 88.7 58.0 86.2 86.5 86.7 86.9 87.1 87.3 87.5 87.7 87.9 88.1 57.5 85.7 85.9 86.1 86.3 86.5 86.7 86.9 87.1 87.3 87.5 57.0 85.1 85.3 85.5 85.7 85.9 86.1 86.3 86.5 86.7 86.9 56.5 84.5 84.7 84.9 85.1 85.3 85.5 85.7 85.9 86.1 86.3 428 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE VII {Concluded) For Use With Baume Hydrometer Calibrated at 60°F. Observed Temperature °F. Observed Degrees 49 48 47 46 45 44 43 42 41 40 Baume Corresponding ; Percent. Hydrocyanic Acid 72.-5 72.0 71.5 71.0 70.5 70.0 69.5 69.0 68.5 68.0 99.7 10) 67.5 99.1 99.4 99.6 99.9 67.0 98.6 98.8 99.1 99.3 99.6 99.8 100 66.5 98.0 98.3 98.5 98.7 99.0 99.2 99.4 99.6 99.8 100 66.0 97.5 97.8 98.0 98.3 98.5 98.7 98.9 99.1 99.3 99.5 65.5 97.0 97.2 97.5 97.7 98.0 98.2 98.4 98.6 98.9 99.1 65.0 96.4 96.6 96.9 97.2 97.4 97.7 97.9 98.1 98.4 98.6 64.5 95.8 96.0 96.3 96.6 96.8 97.1 97.3 97.6 97.8 98.1 64.0 95.3 95.5 95.8 96.0 96.3 96.5 96.8 97.0 97.2 97.5 63.5 94.7 94.9 95.2 95.5 95.7 95.9 96.2 96.4 96.6 96.9 63.0 94.2 94.4 94.7 94.9 95.1 95.4 95.6 95.9 96.1 96.3 62.5 93.6 93.8 94.1 94.3 94.6 94.8 95.1 95.3 95.5 95.7 62.0 93.0 93.2 93.5 93.7 94.0 94.2 94.5 94.7 94.9 95.1 61.5 92.4 92.7 92.9 93.2 93.4 93.6 93.9 94.1 94.4 94.6 61.0 91.8 92.1 92.3 92.6 92.8 93.0 93.3 93.5 93.7 93.9 1 60.5 91.3 91.5 91.7 92.0 92.2 92.4 92.7 92.9 93.1 93.3 ■' 60.0 90.8 91.0 91.2 91.5 91.7 91.9 92.1 92.4 92.6 92.8 59.5 90.2 90.4 90.6 90.9 91.1 91.3 91.5 91.8 92 92.2 59.0 89.6 89.8 90.0 90.3 90.5 90.7 90.9 91.2 91.4 91.6 58.5 89.0 89.2 89.4 89.7 89.9 90.1 90.3 90.6 90.8 91.0 58.0 88.4 88.6 88.8 89.1 89.3 89.5 89.7 90.0 90.2 90.4 57.5 87.8 88.0 88.2 88.4 88.7 88.9 89.1 89.4 89.6 89.8 57.0 87.2 87.4 87.6 87.8 88.0 88.3 88.5 88.7 88.9 89.1 56.5 86.6 80.8 87.0 87.2 87.4 87.0 87.8 88.0 88.2 88.4 STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION No. 230. 242. 250. 251. 252. 25i. 255. 257. 261. 262. 263. 264. 266. 267. 268. 270. 271. 272. 273. 274. 275. 276. 277. No. 114. 115. 117. 124. 126. 127. 128. 129. 131. 133. 135. 136. 137. 138. 139. 140. 142. 143. 144. 147. 148. 151. 152. 153. 154. 155. 156. 157. 158. 160. 162. 164. 165. 166. Enological Investigations. Humus in California Soils. The Loquat. Utilization of the Nitrogen and Organic Matter in Septic and Imhoflf Tank Sludges. Deterioration of Lumber. Irrigation and Soil Conditions in the Sieira Nevada Foothills, California. The Citricola Scale. New Dosage Tables. Melaxuma of the Walnut, "Juglans regia." Citrus Diseases of Florida and Cuba Compared vy^ith Those of California. Size Grades for Ripe Olives. The Calibration of the Leakage Meter. A Spotting of Citrus Fruits Due to the Action of Oil Liberated from the Rind. Experiments with Stocks for Citrus. Growing and Grafting Olive Seedlings. A Comparison of Annual Cropping, Bi- ennial Cropping, and Green Manures on the Yield of Wheat. Feeding Dairy Calves in California. Commercial Fertilizers. Preliminary Report on Kearney Vincr yard Experimental Drain. The Common Honey Bee as an Agent in Prune Pollination. The Cultivation of Belladonna in Cali- fornia. The Pomegranate. Sudan Grass. BULLETINS No. 278. 279. 280. 281. 282. 283. 284. 285. 286. 288. 290. 292. 293. 296. 297. 298. 299. 300. 801. 302. 303. 304. 305. CIRCULARS No. 167. 168. Increasing the Duty of Water. Grafting Vinifera Vineyards. The Selection and Cost of a Small Pumping Plant. 169. Alfalfa Silage for Fattening Steers. 170. Spraying for the Grape Leaf Hopper House Fumigation. 172. Insecticide Formulas. 173 The Control of Citrus Insects. Spraying for Control of Walnut Aphis. 174. County Farm Adviser. 175. Official Tests of Dairy Cows. Melilotus Indica. 176. Wood Decay in Orchard Trees. The Silo in California Agriculture. 177. The Generation of Hydrocyanic Acid 179. Gas in Fumigation by Portable Ma- chines. 181. Thf Practical Application of Improved Methods of Fermentation in Califor- 182. nia Wineries during 1913 and 1914. Practical and Inexpensive Poultry Ap- 183. pliances. 184. Control of Grasshoppers in Imperial 186. Valley. 187. Oidium or Powdery Mildew of the Vine. 188. Tomato Growing in California. 189. "Lungworms." 190. Feeding and Management of Hogs. 191 Some Observations on the Bulk Hand- 193. ling of Grain in California. 195. Announcement of the California State Dairy Cow Competition, 1916-18. 197. Irrigation Practice in Growing Small Fruits in California. 198. Bovine Tuberculosis. 200. How to operate an Incubator. Control of the Penr Scab. 201. Home and Farm Canning. 202. Ijpttuce Growing in California. White Diarrhoea and Coccidiosis of 203. Chicks. 204, Small Fruit Culture in California. Fundamentals of Sugar Beet Culture 205. under California Conditions. 206. The County Farm Bureau. 207. Grain Sorghums. Irrigation of Rice in California. Irrigation of Alfalfa in the Sacramento Valley. Control of the Pocket Gopher in Cali- fornia. Trials with California Silage Crops for Dairy Cows. The Olive Insects of California. Irrigation of Alfalfa in Imperial Valley. The Milch Goat in California. Commercial Fertilizers. Potash from Tule and the Fertilizer Value of Certain Marsh Plants. The June Drop of Washington Navel Oranges. Green Manure Crops in Southern Cali- fornia. Sweet Sorghums for Forage. Topping and Pinching Vines. The Almond in California. Seedless Raisin Grapes. The Use of Lumber on California Farms. Commercial Fertilizers. California State Dairy Cow Competi- tion, 1916-18. Control of Ground Squirrels by the Fumigation Method. Grape Syrup. A Study of the Effects of Freezes on Citrus in California. The Influence of Barley on the Milk Secretions of Cows. Feeding Stuffs of Minor Importance. Spraying for the Control of Wild Morn- ing-Glory within the Fog Belt. The 1918 Grain Crop. Fertilizing California Soils for the 1918 Crop. Wheat Culture. The Construction of the Wood-Hoop Silo. Farm Drainage Methods. Progress Report on the Marketing and Distribution of Milk. Hog Cholera Prevention and the Serum Treatment. Grain Sorghums. Factors of Importance in Producing Milk of Low Bacterial Count. Control of the California Ground Squirrel. Extending the Area of Irrigated Wheat in California for 1918. Infectious Abortion in Cows. A Flock of Sheep on the Farm. Poultry on the Farm. Utilizing the Sorghums. Lambing Sheds. Winter Forage Crops. Agriculture Clubs in California. Pruning the Seedless Grapes. A Study of Farm Labor in California. Revised Compatibility Chart of Insecti- cides and Fungicides. Suggestions for Increasing Egg Pro- duction in a Time of High-Feed Prices. Syrup from Sweet Sorghum. Growing the Fall or Second Crop of Potatoes in California. Helpful Hints to Hog Raisers. County Organization for Rural Fire Control. Peat as a Manure Substitute. Handbook of Plant Diseases and Pest Control. Blackleg. Jack Cheese. Neufchatel Cheese.