172 A. Pedler — Corrosion of Lead Linings of Indian Tea Chests. [No. 3, 



A series of essential oils was then tried, including oils of anise, 

 bergamot, cinnamon, cloves, eucalyptus, lemon, peppermint, and tur- 

 pentine, and also camphor, menthol, and thymol. In almost all the cases 

 of the oils, slight corrosion of the lead into oxide and carbonate was 

 found. It was therefore clear that these oils facilitate the action of 

 moist carbonic acid and air on lead. In no case however had the corrosion 

 proceeded to any large extent, and it consisted only of a kind of white 

 film or bloom on the surface of the lead, such as is frequently seen in 

 tea chests when there appears to have been a tendency to action, though 

 no actual corrosion. In the case of camphor, menthol and thymol the 

 lead was perfectly unacted upon. 



Other tests have been made, but they need not be here described, 

 and so far as my experiments have gone they indicate that the only class 

 of organic substances which is capable of producing rapid chemical ac- 

 tion on tea-lead in the presence of moist air and carbonic acid is the class 

 of fatty acids or the acetic series of acids. Of these formic acid does not 

 produce any carbonate of lead ; the action of acetic acid, as is well known, 

 is violent ; that of propionic acid is of similar nature but less violent : the 

 principal products of the action being in these two cases white lead ; 

 and finally butyric and valeric acids produce yellowish green incrusta- 

 tions on lead which contain only small quantities of carbonate. 



The next point which I have endeavoured to work out is to trace 

 the actual active agent which induced the corrosion in some of the cases 

 described in the first part of the paper, and for this purpose a more 

 minute investigation ^v2is made into the products of the corrosion of the 

 leads. Four of the leads which had been much corroded in the ten sam- 

 ples which had been placed between boards were taken. The num- 

 bers selected were No. 1. Wild mango wood. No. 4. Dumboil wood. 

 No. 5. Julna wood, and No. 8. Sita wood. 



In the corroded lead of No. 1., the material was principally lead 

 carbonate and lead h^^drate ; acetic acid was also distinctly detected by 

 several tests, so that the active agent in the corrosion of this lead 

 was clearly acetic acid. In the corroded lead of No. 4., the material 

 was again principally lead carbonate and hydrate ; acetic acid was also 

 clearly detected, but the quantity present was very minute. In the cor- 

 roded lead of No. 5, again, the corroded material was mainly lead 

 carbonate and lead hydrate ; acetic acid was tested for and detected 

 with great ease, and the quantity was comparatively large, sufficiently 

 large to convert the acid into barium acetate, which presented the usual 

 properties^ but the quantity was not large enough for a quantitative 

 analysis. In the corroded lead of No. 8, the principal material was 

 lead carbonate and hydrate, but the presence of acetic acid was also 

 clearly detected. 



