B.— CHEMISTRY. 4.7 



tinued at the Royal School of Mines until April 1928, when the corrosion 

 section was transferred to the Chemical Research Laboratory. The more 

 outstanding results since obtained are as follows : — • 



Composition of Green Patina on Copper Structures. — Samples of the 

 familiar green patina on exposed copper surfaces, obtained from typical 

 localities, town, country, marine and urban-marine, were analysed 

 completely. Contrary to the general belief, basic copper carbonate was 

 found to be not the principal but only a minor constituent of the green 

 patina. With the exception of the product from a purely marine atmos- 

 phere in which basic copper chloride predominated, the major constituent 

 throughout was basic copper sulphate, and excess of basic sulphate over 

 basic carbonate was greater in the rural than in the urban samples. Where 

 urban and marine conditions coincided, basic sulphate predominated 

 greatly over both basic chloride and basic carbonate. 



It has recently been found that these constituents of the green patina 

 tend to assume the chemical composition of the corresponding green copper 

 minerals. In the limits, the basic copper sulphate of corrosion coincides 

 in composition with brochantite, of which the co-ordination formula is 

 [Cu {(HO),jCu] JSO4, and the basic copper chloride of corrosion with 

 atacamite [Cu -[(HO), CuJ ,] Clj. Basic copper carbonate, on the other 

 hand, tends to assume the composition of malachite [Cu 1(H0).^ Cu}] CO,. 

 Complete agreement with the composition required by the co-ordination 

 theory has been realised in corrosion products after 70 years' exposure and 

 upwards. After shorter periods of exposure the basicity of the product 

 is in a lower ratio than that of the corresponding minerals. 



The complete analysis of these corrosion products entailed special 

 precautions. The carbonates were decomposed by phosphoric acid 

 instead of hydrochloric or sulphuric acid, and any hydrogen chloride and 

 hydrogen sulphide simultaneously set free were eliminated by j9-nitroso- 

 dimethylaniline and copper powder respectively. 



Corrosion of Magnesium Alloys.— The growing use of light magnesium 

 alloys for motor-car and aircraft work has necessitated increased attention 

 to the corrosive properties of these metals. In 1929 a research was begun 

 with the object of discovering improved methods of protection and of 

 learning more about the nature of the corrosion. More than 500 different 

 protective coatings have been produced by chemical means and tested 

 for resistance to sea- water sprays. Of these coatings a few are sufficiently 

 promising to warrant further study. 



Chemotherapy. 

 lu 1927 a joint Exploratory Committee of the Department of 

 Scientific and Industrial Research and of the Medical Research Council 

 decided that there was need for organised research in Chemotherapy, and 

 accordingly the Medical Research Council set up a permanent Committee 

 to advise them on investigations in this field. To this Committee the 

 Department has nominated three chemical members, including the 

 Director of Chemical Research, and facilities have been afforded by the 

 Department for a staff of three chemists to work on problems based on an 

 agreed programme. These chemists have already prepared a considerable 

 number of organic compounds of possible utility in chemotherapy, and 



