TRANSACTIONS OF THE SECTIONS. Gl 



oxide goes on simultaneously with that of the carbonate. The process 

 has been carried out on a scale of considerable magnitude at Birming- 

 ham Heath. The quantity of acetic acid used is less than 1 -300th 

 of the weight of the litharge, and the quantity of moisture found to be 

 most advantageous is such as will just render the litharge sensibly 

 damp to the touch. A purer and more economical source of carbonic 

 acid than bark has been found in the combustion of coke, and power- 

 ful machinery has been applied to facilitate the process, by exposing 

 new surfaces to the action of the gas. The result has been, that the 

 process is completed in as many days of the ordinary one requires 

 months, and the product is of a purer white, and in opacity or body, 

 and all other respects, at least equal to the usual white lead of com- 

 merce. 



One or two other facts deserve mention, which are not generally 

 known. It is singular that if the protoxide of lead known as massicot, 

 and the protoxide known as litharge, be exposed to a high tempera- 

 ture, approaching to a red heat, the massicot will rapidly absorb oxy- 

 gen, and become the ordinary red lead of commerce ; while the same 

 process goes on exceedingly slow with the litharge, if at all ; but, on 

 the other hand, if massicot and litharge be moistened with dilute acetic 

 acid, and exposed to carbonic acid, the litharge will be converted into 

 carbonate before the massicot is much affected. Another fact is, that 

 white lead and oil combine with so much energy, that if linseed oil be 

 poured upon a large quantity of white lead, and the mass be left un- 

 disturbed for a few hours, the temperature will become so elevated, 

 as to carbonize the oil, and render the whole perfectly black. It seems 

 also not generally known, that white lead possesses the power of de- 

 stroying the colouring matter of linseed oil. If sulphate of barytes be 

 mixed with one portion of oil, and white lead with another portion, 

 the latter will appear comparative white. If the two mixtures be 

 allowed to remain for some days undisturbed, a quantity of oil will 

 gradually rise to the surface of both. In the former, the supernatant 

 oil will have undergone no change ; in the latter, the oil will be nearly 

 deprived of colour, and will have acquired the degree of rancidity 

 termed by painters fat. The colouring matter has not combined, as 

 might have been expected, with the white lead, for if this be dissolved 

 by the agency of a weak acid, the disengaged oil will also be found 

 to have been bleached. A large quantity of white lead is required to 

 produce this effect, and the precipitated carbonate is less efficient than 

 the white lead of commerce. 



On Matias Bark, By Dr. Mackay. 



Dr. Mackay read a communication upon a bark which he had lately 

 received from South America, and stated to possess febrifuge qualities 

 equal to those of the best Peruvian bark, for which it has been success- 

 fully substituted. 



Dr. Mackay submitted to the inspection of the Section specimens of 

 two different oils, obtained from the bark by distillation with water, 



