FORTY-FIRST ANNUAL REPORT. 83 



jimonnts beiiio- jnvnrdod in the contest of identifyino- and jnd<;ino' tlie 

 varieties of apples. 



Followiiiji' are the addresses of the senior students: 



r> 



HOW LIME AND SULPHUR KILLS THE SAN JOSE SCALE. 



O. SCHLBUSSNER. 



(Awarded first prize.) 



We have all along known that Lime and Snljthnr spray is the sovereign 

 remedy for the San Jose scale, but I doubt if few of us have ever had 

 any idea of how it did the business or why. All we cared to know was 

 that if we applied it to a tree infested Avith the scale that it did the 

 work, and that after we left that tree all the scale on it were dead. 

 We knew the scale disappeared, but not why it disappeared. 



If any of us had any idea as to the action it was probably an errone- 

 ous one, for it is only in the past year that Dr. George D. Shafer of the 

 experiment station has worked out the true action upon the scale. I 

 know that personally I always thought that there was some sort of a 

 caustic acti(m, and that the scale were sort of eaten up, as by an acid; 

 for I knew that if I got the spray on my hands it would make them 

 sore, and I thought that it Avould act the same way on a scale. Another 

 general view has been that the spray has killed the insect by choking it 

 to death. Almost all insects breathe by small pores or openings in 

 their sides, called tracheae, and it was thought by many that the mixture 

 got into these and plugged them up, and thus caused choking, just as 

 we would be choked to death if some one were to plug up our nose and 

 mouth with sealing-wax. As a matter of fact, the Lime and Sul]»hur 

 s]»ray does destroy the insect by suffocation but in a different way than 

 the one which I have described. 



In order to understand how it works, we must first have some idea 

 of the nature of the spray itself. We all knoAV that when we boil the 

 lime and suli)hur together to make the spray, that when we have 

 finished we have something different than what we started out with 

 — that is that we have a chemical combination of lime and sulphur — - 

 not a mixture of them but something quite different than either of them. 

 In the same way Ave might say that we eat beef and potatoes, we keep 

 them in our bodies, but they are changed and now are no longer beef 

 and potatoes but human flesh, blood and bones. 



What we have in the case of the boiled lime and sulphur, is a com- 

 pound known as Polysulphides of Calcium. This compound has the 

 proper t3' of taking oxygen from the air to make it form calcium thio- 

 sulphate, after which it takes up more oxygen, forming suphites of 

 calcium, and as a final step forms sulphates of calcium again taking 

 up oxygen to do this — in every step taking up always more oxygen from 

 the air you will notice. 



A knowledge of this property led to some experiments to determine 

 exactly how much oxygen was taken up, and by placing a filter or 



