the resultios; mixture contains about 13.5 volumes of available oxygen, and its bacte- 

 ricide power still remains the same as the bactericide poAver of sample No. 5, which 

 contains 16.55 volumes of available oxygen. 



Sample No. 14 comes next to sample No. 5, but it is readily seen that that the de- 

 gree of acidity is entirely too large for a preparation which is to be applied to the most 

 sensitive diseased mucous membranes. , 



Sample No. 11, called " Pyrozone " which contains 11.20 volumes of available oxy- 

 gen, is quite similar to sample No. 6, with the exception that the latter contains a 

 small quantity of salicylic acid. Very likely the salicylic acid has for its ohject to in- 

 crease the bactericide power, but, unfortunately, I fear tliat it impairs the keeping 

 properties ot this preparation. 



Acidity. — The 14 brands which I have examined contain free acids (phosi)horic, 

 sulphuric, muriatic ;) and 1 must say that peroxide of hydrogen medicinal should 

 never be made neutral before using, even in the most delicate cases. Neutral peroxide 

 of hydrogen rapidly decomposes under all conditions of exposure. 



The keeping properties of H2 02 solutions vary a great deal with the degree of 

 purity and the percentage of free acid contained therein. 



If the proportion of acid is too large, the profession well know that it acts as an irri- 

 tant upon diseased surfaces. If it is too small, the solution does not keep well. 



My opinion is, that a standard solution of medicinal H2 02 must answer the follow- 

 ing tests : 



1. It should contain at least 15 volumes of available oxygen. 



2. The quantity of free acid contained in 100 cubic centimeters should require not 

 less than 1 c. c. and not more than 3 c. c. of normal volumetric soda solution, to be 

 made \|eutral. Such a small quantity of free acid is not objectionable. 



3. It should not contain any soluble baryta salts. 



4. It must be free from sediment. 



It is to be noticed that the brands No. 7 and No. 12 are valueless. 



The brands No. 8 and No. 9 are not fit for medicinal uses, owing to the fact that 

 they contain traces of soluble baryta salts. 



The brand No. 3 has heavy sediment of sulphate of baryta, which may be considered 

 inert towards the system, but it is certainly detrimental to the keeping qualities of 

 this prenaration. 



Brand No. 14, which is sold as a ten volume solution, is really twelve volumes, but 

 it is too acid. Brand No. 5, which is sold as a fifteen volume solution, is really 16.55 

 volumes, viz.: About ten per cent above the standard. 



The brand No. 2, which is sold without any mention of volume, is really a 27.35 

 volume solution, viz. : Ninety per cent above the standard. 



None of the otiier brands come up to the standard, but on the contrary they run 

 from 35 to 55 per cent below. 



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ONE GIVES RELIEF. 



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