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R. H. Richards—Jet Aspirator for Laboratories. 427 
From Prof. J. Lawrence Smith, I learned a few days since, 
that a metallic jet aspirator is used in France. e maker and 
the particulars of its form he did not recall at the moment. 
In the store of Messrs. Codman & Shurtleff of Boston I find 
an instrument called a saliva pump, made to be screwed to the 
hydrant at any point. This instrument, while it is essentially 
the same as mine, differs in obtaining its foam in the cone a 0, 
fig. 3, by an obstruction which is introduced at o. The cone ao 
is much too acute, according to my experience, but I should 
judge that it would do fair work, and for its present application 
is just as good as if it had the most economical form. This 
instrument was invented and is now made by Dr. J. K. Fis 
of Salem, Mass. 
Mass, Institute of Technology, Boston. 
Note.—Since writing this account, I have given dimensions 
and rules for the manufacture of these aspirators, to suit ap- 
proximately any head of water, to Mr. EK. B. Benjamin, 10 
d—c a—b 
o(1 ei aa) : a(1+ —) = 1 atmosphere : atmospheres of water 
ressure, 
a+a ae 
"760 _ § atmospheres of 
d—c | water pressure. 
ae 
