No. 6. DEPARTMENT OF AGRICULTURE. 477 



these samples of lead arsenate which was found to be the case. For 

 example it was found that lead arsenate as it comes into the markets 

 usually contains the pyroarsenate, which is soluble in ammonia and 

 the acid arsenate which are stable under acid conditions, but under 

 neutral and alkaline conditions these change into the orthoarsenate 

 the most stable compound, with the liberation of arsenic oxide or 

 an alkaliarsenate, which are soluble in water and destroy foliage. 

 From this is appears that when arsenate of lead, if prepared for 

 spraying in water containing alkali salts, or when it is exposed on 

 the surface of the leaves, the action of the neutral water of fogs and 

 dcAvs that the pyroarsenate and the acid arsenate change into the 

 orthoarsenate, liberates arsenic oxide or an alkali arsenate which, 

 because of its solubility, is taken into the leaf and the leaf tissue 

 destroyed. Therefore, the orthoarsenate is the only compound that 

 should be used in spray mixtures, and it has been found wherever 

 this substance has been used in the pure state no burning of foliage 

 has taken place. As already stated, the pyroarsenate of lead is 

 soluble in ammonia, and also that when the arsenate is exposed to 

 neutral water and water containing alkali salts, it changes 

 into the orthoarsenate of lead with the liberation of arsenic oxide or 

 an alkali arsejiate. If, therefore, there is any pyroarsenate or acid 

 arsenate of lead present in a sample of lead arsenate the only thing 

 necessary is to take a sample of half an ounce or an ounce macerate 

 it and mix with about a gill of water in a granite or porcelain lined 

 vessel. Then add as much strong amomnia as water and mix again 

 and heat slowly and mix while heating and finally bring the sub- 

 stance to a boil. Set aside and allow the mixture to settle and cool, 

 and then pour the clear solution through a filter into a funnel. Boil 

 the solution until about all the ammonia is driven off. To the 

 solution that remains after the ammonia is driven off add acetic 

 acid or strong clear vinegar until it is distinctly acid, then a clear 

 strong solution of lead acetate or sugar of lead, to which a little 

 acetic acid or vinegar has been added, if a white precipitate forms 

 when the solutions come together or are shaken up together, theji 

 the sample of arsenate or lead contains arsenic oxide or a solution ar- 

 senic and will burn the foliage of fruit trees. 



Here it seems we have at last an arsenical that can be prepared 

 in such a way that it will not burn foliage. 



ADDRESS OF DR. SPARKS 



I am sorry I could not spend more time with you today, but I spent 

 most of my time in the Department of Health, trying to convince them 

 that I knew better where a sewage disposal plant should be located 

 than they did. I have been beaten, I may as well confess, so I will 

 turn to a more pleasant subject. 



What can we do to disseminate more information to the common 

 people? How can we bridge over the chasm between the people and 

 the college and the experiment station? We have tried bulletins, 



