There have been several specific cases of damage during the last 5 or 6 years, in which large quantities of tea and of several other delicate substances have been damaged, and it has been possible to make a much more complete investigation into the cause than could be made when the number of damaged packages was but small. One serious case was a consignment of Assam tea, which, instead of its proper tea flavour and smell, had a distinctive character of its own, the smell resembling a new and excessively rank kid glove. Some hundreds of chests were damaged in this way, and after inquiry it was found that for 3 or 4 seasons in succession a large portion of the tea from this particular plantation had come over damaged in a similar way, although to a less extent. The tea itself, the mode of packing it, and the temperature at which it was packed, naturally suggested themselves as the cause, but careful inquiries proved that the manipulation in the curing of the tea was just the same as in other surrounding plantations, that there was apparently no difference in the temperature of packing, and that the cause must be looked for in something further than these.
A number of the chests were examined, and it was found that they were made of a mixture of different kinds of wood, one chest containing sometimes as many as 6 or 7 different species - in fact, frequently one-half the lid would be of one wood and the other half of another wood. When the wood was removed from the lead lining, the inner surface of some of the pieces was in its normal condition, nearly clean and free from smell, while other pieces were coated with a whitish powder, in some cases in quantity so small as to need a pocket lens to see it - in other cases in larger quantities, so that it could be scraped up with a finger or a card - and the lead beneath these, pieces of wood which had the white powder on was found to be pitted or indented on the surface, and in cases where the action had proceeded to the fullest extent it was perforated as finely and almost as regularly as if the whole had been pricked with a needle. The lead itself was examined. It was common lead, containing only 1/4 to 1/2 per cent. of antimony, and quite as good as, if not superior to, a large quantity of lead which was used for other consignments in which no deficiency had occurred.
The white powder was then collected in sufficient quantity, and found by analysis to be white-lead of normal composition, i.e. about 75 per cent. lead carbonate, 25 per cent. lead hydrate, with small traces of adhering acetic acid. This points clearly to the question which has to be decided as to the mode in which the damage has been effected. So far we have cases lined with lead, which in some parts are coated with white-lead on the exterior surface of the lead, and perforated, and in other parts are not; secondly, the coating of white-lead and the perforation for the greater part accord in position with certain pieces of wood forming part of the chest, while the less injured part of the lead accords in position with other portions of the wood forming the chest; and thirdly, we have the objectionable smell. To see in what way this is produced, we must refer to the chemical reactions which can take place.
The ordinary Dutch process for the manufacture of white-lead is so well known that it is only necessary to sketch it in outline to show its reference to this case. When tan or dung, both of which are essentially woody fibre, although in both cases containing an excess of nitrogenous matter, are exposed to moist heat, carbonic acid is generated. The generation of this carbonic acid depends upon conditions which involve the presence of moisture and a moderately warm temperature. Minute quantities of acetic acid are added in starting the stack, but the proportion is very small, less than 1 per cent. on the quantity of lead stacked, and all this is usually absorbed or combined with lead before 1/10 of the lead has been corroded. It is obvious that there is no special virtue in the materials used for this Dutch process, so long as lead is exposed to an atmosphere which contains acetic acid in minute traces. and carbonic acid in very small quantity. This air, so saturated, is capable of acting upon lead and producing the effect now referred to. The sap of wood invariably contains sugar. The quantity is small, but still measurable. This sugar is, in every case that has come under observation, a fermentable sugar, and the first result of the fermentation is in most cases alcohol.
Fermentation being carried a step further, free acetic acid is the natural result. With the formation of acetic acid carbonic acid is also formed, and it is a general - perhaps universal - thing that carbonic acid is generated or liberated from substances in the hold of a vessel. Transferring this from a theoretical to a practical case : A wood containing sap which was more than usually saturated with sugar, and exposed to a moist heat, would ferment more readily, would produce a larger quantity of alcohol, would consequently produce a larger quantity of acetic acid, and would therefore, by inference, derived from practical work, produce a larger amount of carbonic acid, and thence of white-lead. These effects would be produced mainly, if not entirely, upon the surface of the wood, and one of these surfaces would be in contact with the metallic lead which forms the lining of the case. Now let us see what would take place. The lead lining would be exactly in the same condition as the lead in a lead-stack which was being worked by the Dutch process. Acetic acid, carbonic acid, and moisture would all be p esent.
There would be a reasonable and probably, in accordance with practice, a very proper degree of heat, and the lead and wood would be in contact; and it seems the most natural thing in the world to assume that, as the result, lead acetate would be formed by the direct action of the acetic acid. Lead carbonate and hydrate would be formed from this by the action of the carbonic acid and the moisture in the air, and although the two chemical changes would run on almost concurrently, yet the result would be the direct formation of a film of white-lead. Again, the white-lead having been formed, the sheet lead forming the lining has necessarily been wasted - part of it has been transformed, to put it in a plain way, from metal into paint.