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,