apjJfjpiVERSlTY UNIVERSITY OF CALIFORNIA. AGRICULTURAL EXPERIMENT STATION. BERKELEY, CAL. E. W. HILGARD, Director. BULLETIN NO. 79 Experiments on the Cause and Avoidance of Injury to Foliage in the Hydrocyanic Gas Treatment of Trees. In^ University Experiment Station Bulletin No. 71, it was shown that hydrocyanic acid gas could be used effectively against scale in- sects; but that the tree suffered by the treat- ment. In a subsequent bulletin (No. 73), it was shown that the injury to the foliage of cit- rus trees could be prevented by the use of car- bonic acid gas, injected at the same time with the hydrocyanic. The cause of this preventive action was not readily explained and its failure to protect on very hot days, showed that something remained to be done in perfecting the treatment; furthermore, the additional trouble and expense of this improved treatment made it highly desirable to seek for some easier means of saving the foliage. The investigations here recorded were made from time to time during November, December and January of 1887-8, in order to find out what caused the injury, and likewise to ex- plain the protective action of the carbonic acid used in the later experiments. The general man- ner of treatment as applied on a large scale, was followed in each operation;* and suita- ble apparatus was devised for carrying out the details. A barrel of about five cubic feet ca- pacity was used as a chamber to replace the tent. A small bellows was used to produce the necessary circulation, and a glass bottle, into which was inserted a closed funnel holding the proper doses, served as a generator. A small Woulffs (three-necked) bottle served the pur- pose of a "relay," where the gases could be *It shou'd be noted that an essential point in the mode of operating, first practiced by me at San Gabriel in the spring and bumraer of 1S87, was the use, at the sugges^ tion of Prof. Hilgard, of a pump or blower for the pur- pose of mixing the gases generated, with the air in the tent, by continuous circulation; thus avoiding injury ironi the effect* of overdoses at some points while leav- ing others without adequate treatment, as must inevita- bly hippen where no such equalizing appliance is used. It was doubtless from this caufe that experiments pre- viously made by others (understood to have employed hydrocyanic gas) were not satisfactory. mixed, or material for drying them inserted. The temperature was indicated by thermome- ters placed in the top of the chamber. A half-doz3n orange branches set in pots, and a doz3n well-potted orange seedlings, were used to experiment upon. The former were used to obtain some preliminary measure of the quanti- ty of materials to be employed in the later treatments. Tub following table shows the arrangement of the several experiments ', numbered for referkbcf. 1 Not treated 2 Cyanide Wet 3 Cyanide + Carbonate... Wet 4 Cyanide ply 5 Cyanide + Carbonate... Dry 6 Cyanide I Wet 7, Cyanide |Wet 8 Cyanide -f Carbonate. . . Wet 9 Cyanide Dry 10 Cyanide + Carbonate. . . Dry HCjanide Wet 12 Cyanide + Carbonate. . Wet 13 Cyanide Wet 14 Cyanide + Carbonate. . . Wet 15 Cyanide Dry 16 Cyanide + Carbonate. . . Dry 17 Cyanide Wet 18|Cyanide + Carbonate... Wet 19 Ammonia determination 20 Cyanide Dry 21 Cyanide Dry 22Cyani''e Wet 23 Cyanide Wet 24 Cyanide Wet 25 j Cyanide Wet 26;Cjanide Wet 27iCvanide + Ammonia. .. Wet 2*|Cyanide + Ammonia.. . Wet 29 Cyanide + Ammonia. . . Wet 30 Formic Acid -f Ammonia 31 (Formic Acid I 67 64 Sprayed. 63 Spraved. 100 I 103 109 | 106 102 97 Sprayed. Sprayed. Mixed in chamber. The second column shows the material em- 2 ployed; the third indicates whether they were used in the solid condition (dry), or in solution (wet). When operating in the " dry" way the salts were used in the solid form, and usually the gas was further dried and freed from ammonia by passing it through strong sulphuric acid. In operating in the " wet" way, solutions of the salts were used and the gas was passed directly into the chamber, except in one or two cases where the gas was subsequently dried. The fourth column indicates the temperature at which the air in the chamber was kept. In No. 1 an orange limb was used, potted like the others and left untreated to serve as a check. It remained in good condition through- out the time of experimenting. In the numbers following, the conditions were varied both by changing the manner of treatment and materials used. The doses used were larger in proportion than those used in field-work, in which it was shown that small trees required proportionately larger doses than large ones. In several cases the trees and the inside of the chamber were sprayed with water, to note the effect of the gas upon wet trees, and also to note that of the water upon the gases them- selves. Production and Effects of Ammonia. It is known that when cyanatea are present in generating hydrocyanic gas, more or less am- monia is produced. In the materials used for these experiments, this may have been the case. Furthermore, under certain conditions, ammonia may be produced in the treatment of simple cyanide with acid. Preliminary tests were made to demonstrate these facts, and to study the reactions when applied in various ways, as well as to determine the best mode of using the materials. For the intense scalding effects of ammonia upon the foliage had been noted in my former experiments (see Bulletin No. 71), and it was conjectured that this gas, unintentionally produced, might be concerned in causing in- jury in cases not otherwise easily explained. As previously reported, it was found im- practicable to use the cyanide of potassium without first dissolving it, and that it was nec- essary to keep the carbonate of soda well mixed with the cyanide, so that the reaction upon both would occur at the same time. But it was further shown that the alkaline reaction of the gas, due to ammonia, is produced only when the solution, instead of the solid cyanide, is used; rapid addition of the acid to the dry salt, or vice versa, invariably produced an acid gas, while the slow mixing of the two materials in solution invariably produced decided alkalinity, often to a very harmful degree. The amount of ammonia was found to be variable, perhaps largely because a part was masked by the hy- drocyanic acid produced during the violent action that takes place when the acid is added rapidly to the solution. All the experiments with the dry cyanide alone showed but *l ; ght injury to the foliage, and a slightly increased injury was noted on the plants treated with/the cyanide solution alone. When the carbonate of soda was used with the cyanide in the solid form or in solution, the injury to foliage was in either case very ma- terially lessened. Passing the gas through sulphuric acid produced results similar to those of the carbonate treatment, viz.- immunity to the foliage. Indications having thus pointed toward am- monia as the cause of the injury, some direct experiments were made with this gas. In the first ammonia-treatment the gis w as separately generated and mixed with the hydrocyanic gas from an ordinary treatment, the mixed gases being conducted into the chamber. The intensely acid action of the gas leaving the hydrocyanic generator at once turned to the alkaline, and so continued in the chamber, thus showing that a certain moderate excess of ammonia was present. Decidedly injurious ef- fects upon the foliage were quickly noted. In this experiment the ammonia and cyanide gases were mixed in the relay." In order to leave more of the ammonia free to act upon the foliage, it was injected directly into the cham- ber, where the two gases were less intimately mixed. Upon circulating the gas, strong alka- linity prevailed in all parts of the apparatus and the atmosphere about the tree w.is decidedly charged with ammonia. The results were very marked. In a short time the trees wilted; in 10 days all the foliage was crimped up and later all fell off. Even the wood of the more tender branches was noticeably affected. As formic acid is often produced during the decomposition of a cyanide, an experiment was made to determine its effect upon foliage. A solution of the acid was boiled and the vapor was i conducted intr> the chamber until a quite decided acid reaction wa* shown by the test papers. No harmful effect was noticeable. For- mic acid and ammonia were next separately in- troduced, the ammonia being in very slight ex- cess. In this case also no noticeable harm was done. Influence of Temperature. It is to be regretted that the normal tempera- ture (50 3 to 65 3 F.) during the experiments was much lower than that which would be met with in actual field-work; and therefore the injury done to the seedlings would not be so marked as in the latter case. An attempt was made to raise the tempera- ture within the chamber up to that of a warm summer's day in the orange district?. The range of temperatures used was 95° to 105° F., but the outside temperature being low, as soon as circulation began, the moisture from the in- terior of the chamber, given off during the rise in temperature, was partially drawn in and condensed in the tubes during" the circulation, and thus absorbed the ammonia as well as part of the hydrocyanic gas. Notwithstanding this partial removal of am- monia by absorption, the results showed that these high-temperature treatments produced more injurious effects than similar treatments at lower temperatures. Conclusions. From the foregoing experiments we are led to believe that ammonia has been the fruitful cause of the injury to the trees eulj jeted to the treatment under discussion. Under this view of the case, the beneficial effects of the use of carbjnic acid gas would seem to be due to its power of neutralizing the ammonia, with the formation of carbonate of ammonium, when the 3 two gaees come together. And, furthermore, the failure of the carbonic acid to completely preserve the tree during the hot part of the day follows from the easy decomposition, by heat, of the carbonate of ammonium, which does not occur during treatments at lower tem- peratures. Even the formate of ammonium, produced in a preceding experiment, would be decomposed in a like manner and seme am- monia set free to act upon the foliage. Modes of Preventing Injury. There are, then, two means of averting the injury to the foliage: First, by the use of the dry salt; second, by the use of proper appli- ances to absorb the ammonia as it leaves the generator. In the first case, viz.: Using the dry salt$ only a minimum amount of ammonia is pro- duced during a strong reaction. But it was shown that it is quite impossible to handle the dry salt so as to insure complete action of the whole dose; and furthermore, the slowness of the action prevents the rapid injection of the gas into the tent. It should be injected rapidly so that complete circulation of the gas about the tree may be established and the maximum effect produced at once, so as not make it nec- essary to increase the time of exposure. In the second case, viz.: the use of the solution, the action i9 rapid and the injec- tion can take place immediately. But with the use of solution, the trouble from for- mation of ammonia comes in. This can loe obviated by the use of the proper apparatus to absorb the ammonia as it leaves the generator. The apparatus used in field-work can be so nfodified that an absorbent of the ammonia may be inserted at the exit of the generator and connected with the general circulation. Such an apparatus can be made of a cylinder filled with loose pumice-stone over which sulphuric acid is poured from time to time. By this means a large surface is exposed for the absorp- tion, and it can be readily so arranged that with slight trouble the surface of the pumice- stone can be re-saturated with sulphuric acid. This apparatus, if interposed in the tubes through which the general circulation takes place, would interfere with the rapid passing of the volume of air which is to accomplish the agitation within the tent. In order to avoid this obstruction, a secondary circuit may be connected with the general circulation, to be used only when the generator is to be cleared of the last portion of the hydrocyanic gas. The pressure of the gas alone during its evolu- tion is sufficient to force its way elowly into the general circulation. Thus the general cir- culation and agitation remain independent of both generator and drying-chamber. The sec- ondary circuit carries a volume of air from the blower through the generator and through the drying-vessel and thence discharges into the general circulating pipe. This is accomplished by placing a hinged valve at the exit opening of the blower into the circulating tube in such a manner that the current of air may be passed either forward or backward by reversing the motion of the blower. The air may be forced by the backward movement through the sec- ondary circuit. By "the application of either of the above methods the use of carbonate of soda can be avoided, and the work somewhat simplified. There will ba far less residue in the generator, so that several treatments may be made with- out emptying the litter. Beside this there will be a decrease in the expense through the omission of the carbonate and the correspond- ingly less amount of sulphuric acid required. It will be necessary to demonstrate by further experiments whether the use of the cyanide alone will be so effective against the scale as when combined with carbonic acid. The best results of field experiments have accompanied the joint use of carbonate and cyanide, although it is maintained that the cyanide alone will pro- duce as fatal effects upon the insect. Some tests were incidentally made to note the effect of the gas upon the scale insects Aspidio- tiw and Lecanium. Branches of laurel and acacia infested with these scales were placed in the chamber during the treatment of trees at higher temperatures. The effect in some in- stances was complete, while in others 90 per cent of the insects were killed and the remain- ing 10 per cent still showed faint signs of life and may have survived the treatment. Under the proper treatment this gas remedy will undoubt- edly prove as effective on these scales as upon the white scale, against which the remedy was originally intended to be applied. Berkeley, May 5, 1888. F. W. Morse,