31 



The prescribed doses for small trees will be found too small, unless the trees are very 

 low. The calculations are all based upon the supposition that the trees are nearly spher- 

 ical in shape; but in most cases it will be found ihat the trees of small dimensions have 

 most of the branches raised fully four or five feet from the ground, thus leaving a large 

 volume on the inside of the tent unoccupied. Due allowance must be made when the 

 height of the tree is so much greater than its diameter. 



Mode of Operating. 



Place the desired amount of acid in the acid receiver, then put the required amount of 

 soda in a convenient vessel (a gallon measure serves the purpose well), and add water to 

 bring it to a thin paste, stirring well to get rid of all the lumps, before the cyanide solu- 

 tion is added. Mix the cyanide solution and the soda paste so that the undissolved soda 

 will remain evenly distributed throughout the mixture. Pour into the cyanide receiver, 

 and allow it to run slowly and regularli/ upon the acid which has previously been run into 

 the generator. As soon as the cyanide solution begins to enter the generator, the blower 

 should be turned slowly, and continued until all the material is run in and violent action 

 ceased. This usually takes a minute or so after the materials have united. Then follow 

 with violent blowing for a minute or so, and allow to rest until about fifteen minutes from 

 the beginning of the treatment, when violent blowing is repeated for one minute. The 

 time occupied in running in the mixture should be about as follows for the different sized 

 trees : 



10-foot tree - 4 minutes. 



11-foot tree - - - 5 minutes. 



12-foot tree. --- 5.5 minutes. 



13-foot tree. , -- — -- 6 minutes. 



14-foot tree. - -- 7 minutes. 



15-foot tree 7.5 minutes. 



16-foot tree - -- 8 minutes. 



17-foot tree --. 9 minutes. 



18-foot tree .- --- 10 minutes. 



It is quite important that the time of injecting shall be closely observed, and should be 

 lengthened rather than shortened. No time will be saved by hurrying this partof the treat- 

 ment, for if run in too fast lumps will be formed which will take some time to be com- 

 pletely acted upon by the acid. If the time is slightly lengthened no serious results will 

 follow. Some of the largest doses have been completelj' acted upon in less than fifteen 

 minutes, thus making it possible for a single generator to serve two tents when the pre- 

 scribed time of exposure is adopted. It is advisable to continue the treatment of a single 

 tree for about thirty minutes, although the time may be slightly shortened when two tents 

 are used. 



This method can be used when the temperature does hot rise much above 

 70 degrees F., but when it becomes much higher it will affect the foliage. 

 To avoid this trouble it is suggested to do the work during the cooler por- 

 tion of the year. 



Dry Gas Process. 



In Mr. Coquillett's report to Professor Riley in reviewing the different 

 processes is favored the method of passing the gas through sulphuric acid, 

 which method he describes as follows, under the name of the dry gas, his 

 idea being that the damage done by hydrocyanic gas, when generated, is 

 due to moisture which carries particles with it: 



I have already alluded above to the fact that the drier the gas the less iniurious was 

 the effect upon the tree confined in it; and it occurred to me that the gas mi^ht be gener- 

 ated in the usual way, by acting with sulphuric acid upon potassium cyanide dissolved 

 in water, and afterward be dried by passing it through some medium that would deprive 

 it of its moisture. Knowing the great avidity of sulphuric acid for moisture, I cleter- 

 mined to use it as a drier for gas, and several tests which I have made with this gas dried 

 in this way prove that it does not injure the foliage of orange trees confined in it, while 

 it is just as fatal to the scale insects as is the moist gas. The density of the acid through 

 which the gas had passed was lowered about one degree, as indicated by the hydrometer ; 

 but this would not prevent its use for generating the gas. 



The cyanide is dissolved by boiling in water for a few minutes, using one gallon of 

 water for each five pounds of "cyanide. It is desirable to use as little water as possible for 

 this purpose, but the quantity could not be very much reduced from that given above. I 

 have tried to dissolve five pounds of the cyanide in half a gallon of water, but all of the 

 cyanide had not dissolved after half an hour's boiling. For every ounce of the cyanide 

 solution use half an ounce of sulphuric acid, but it is always desirable to add some of the 

 acid to the prescribed dose, in order that there may be an excess of the acid. No evil 

 results will follow if double the proper quantity of the acid were to be used, whereas if less 



