204 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



penicillin from the charcoal j the extract is evaporated, acidified, and 

 treated with ether. Various procedures for large-scale production and 

 recovery of penicillin have been described (503, 607, 768). 



Various modifications of these methods may be employed. In some 

 cases, «-butyl alcohol is used for extraction. The culture filtrate is ad- 

 justed to fH 6.4 and ammonium sulfate added, and the penicillin is 

 extracted. When light petroleum ether and dilute sodium bicarbonate 

 solution are added to the butyl alcohol extract, the penicillin is brought 

 back into aqueous solution (48). The problem of drying is very im- 

 portant (276). 



The barium salt was at first considered as the most suitable form for 

 general use. In this form, penicillin retains its antibacterial activity for 

 an indefinite period. It is soluble in absolute methyl alcohol but in- 

 soluble in absolute ethyl alcohol. However, the Na and Ca salts are the 

 common forms now used. Penicillin forms water-soluble salts with most 

 heavy metals, except Fe"^+. 



Penicillin is unstable and readily inactivated by a number of reagents, 

 including heavy metal ions, especially Cu, Pb, Zn, and Cd. Penicillin is 

 stable toward light and atmospheric oxygen, but is oxidized by H^Oo 

 and KMn04, the antibacterial activity being lost. 



In assaying penicillin, both biological and chemical tests are used. Of 

 the former, the cup assay method is most commonly employed, al- 

 though the turbidimetric and other tests are also frequently used. The 

 different forms of penicillin are recognized by the differences in their 

 effect upon various bacteria, notably S. aureus and B. subtilis. 



The world standard for penicillin has been defined as that activity 

 which is present in 0.6 micrograms of the international penicillin stand- 

 ard (384). One mg. of crystalline penicillin will thus contain 1,667 

 Oxford units (O.U.) and will be comparable to 84 million dilution 

 units against S. aureus (168, 454). 



The chemical method for assaying penicillin is based upon the acidity 

 produced by the action of a standard penicillinase solution upon the 

 penicillin preparation and titrated to ^H 8.0 {666). The colorimetric 

 method is based upon its interaction with an intensely colored primary 

 amine, N-(l-naphthyl-4-azobenzene)-ethylenediamine to give amidic 

 products containing acidic groups (845a). 



