REPORTS OF OBSERVATIONS AND EXPERIMENTS. 31 



make a series of experiments with these two gases. Accordingly, during 

 the mouths of March and April of 1803, I carried out such a series of 

 experiments, the results of which but confirm my previous stateim 

 to the effect that both in regard to the expense and effectiveness 

 hydrocyanic-acid gas is preferable to either of the two gases men- 

 tioned above. 



For the production of sulphureted hydrogen I used iron sulphide 

 (FeS), commercial sulphuric acid (H 2 S0 4 ), and water. The iron 

 sulphide was obtained for 20 cents per pound, aud requires about the 

 same quantity of sulphuric acid and water that potassium cyanide 

 requires in the production of hydrocyanic-acid gas. The sulphide was 

 partially pulverized, and none of the pieces were over one-eighth of an 

 inch in diameter. When the acid was added to the sulphide, no action 

 took place, but as soon as the water was added, quite brisk action at 

 once began, with evolution of the ill-smelling gas. The action of the 

 acid and water upon the sulphide was very much slower than their 

 action upon potassium cyanide, even when the latter is used in large 

 pieces. The tests were made during the month of March, from about 

 9:30 o'clock in the forenoon to about noon of different days, when the 

 weather was comparatively cool. 



When used so strong that its cost about equaled that of potassium 

 cyanide used for the purpose of generating hydrocyanic-acid gas, the 

 resulting sulphureted hydrogen was fatal to a very small percentage 

 of the insects (Lecanium hesperidum and L. olecv) on the orange trees 

 experimented upon, and the leaves upon these trees were not injured 

 by the gas. Here I used about three times as large a quantity of the 

 sulphide as would have been required of the cyanide to destroy all the 

 insects of the tree, but it was scarcely one tenth as effectual as the lat- 

 ter, and I therefore considered it would be quite useless to continue 

 experimenting further with the iron sulphide. 



I had in previous years generated arseniureted hydrogen by acting 

 upon small pieces of sheet zinc with commercial sulphuric acid in the 

 presence of an aqueous solution of white arsenic (AS..0 3 ), but as this 

 is a somewhat imperfect method I decided to test the method of gen. 

 crating this gas by acting with water and sulphuric acid upon zinc 

 arsenide (AiS 2 Zn 3 ). Failing to obtain the last-mentioned substance at 

 any point on the Pacific coast, I was under the necessity of having it 

 manufactured expressly for my use. Accordingly I made the neces- 

 sary arrangements with Wade & Wade, manufacturing chemists of 

 Los Angeles, Cal. The arsenide is manufactured from metallic zinc 

 and arsenic, one and three-tenths parts of the former being used to one 

 of the latter. The price of metallic arsenic in San Francisco, is 50 

 cents per pound, and of granulated zinc, 60 cents. The two metals 

 in the proportion above given were placed in a crucible along with a 

 small quantity of powdered charcoal, and the crucible closed and sub- 

 jected to the heat of an assayer's furnace for a space oi' about twenty 



