Under • those circumstances, the paraffin-oil acts even less energetically, and though traces of the metal may be found in the oil in an hour from the commencement of the experiment, yet it takes about a week before the oil becomes largely impregnated with the metal. (4) Tin.-This metal is very slightly acted upon by the oil, and in a month's time the amount of metal dissolved in and diffused through the oil is very small, and is not sufficient to impede the combustion of the oil in lamps. (5) Copper. - A very slight action is apparent after a month's exposure, and practically the oil is not affected thereby as a luminant. (6) Iron is slightly affected by the paraffin-oil, and on 10 days' contact the oil becomes deeper in colour and throws down a fine ferruginous sediment. The oil itself is, however, not materially injured as an illuminating agent. (7) Zinc.-This metal is sensibly acted upon by the paraffin-oil, and the latter retains the zinc compound in solution and suspension. The oil is decidedly injured as a luminant. (8) Tin solder of the best quality, containing 2 parts tin and 1 of lead, is acted upon by the paraffin-oil, and the latter is injuriously affected as an illuminating agent. (9) Tin soldered with tin solder is also acted upon, and lead is dissolved out from the solder by the paraffin-oil. The quantity of metal dissolved out is not large, but is sufficient to influence the oil as a luminant. (10) Tinned copper is not practically affected by the paraffin-oil so far as the combustion of the oil is concerned, but traces of both the tin and the copper are found in the oil after a month's exposure. (11) Tinned iron is acted upon very slightly, but the oil does not suffer as an illuminating agent (12) Galvanized iron is readily acted upon by the oil, and the quality of the oil for burning with wicks is sensibly injured.

These experimental observations demonstrate that the metals lead and zinc should not be employed in the construction of or in the lining of cisterns or other vessels intended for the storage or reception of paraffin-oils; that the metals tin, copper, and iron, as well as tinned copper and tinned iron, may be safely employed in the fabrication of the cisterns or other vessels; and that ordinary tin solder containing lead should not be used in the soldering of such cisterns or vessels. Galvanized iron should likewise be avoided. Whilst stating that the cisterns or vessels for the retention of paraffin-oil may be safely constructed of or be lined with tin, copper, or iron, it would be preferable to use cisterns or vessels lined with enamel in the interior, provided such could be obtained of sufficient size for the purpose. The ordinary enamelled iron pots present absolutely no surface upon which the paraffin-oil can act, and cisterns or vessels constructed in a similar way, with an interior lining of enamel, would retain the paraffin-oil for any time without affecting in the slightest degree the purity of the oil or its entire suitability for illuminating purposes.

In cases where leaden cisterns or vessels have been in use for the retention of the paraffin-oil, there can be no doubt that the inferior illuminating power of the oil may be fairly attributed to the lead impregnation. The action is lessened much by washing over the surface of the lead with dilute sulphuric acid, which forms a coating of the insoluble lead sulphate, in or through which the paraffin-oil has comparatively a feeble action. The oil, however, does take up a little lead, and hence the impurity still continues to pass to the wick. A better protective coating is obtained by brushing over the surface of the. lead with solution of sulphuretted hydrogen, and still better with ammonium sulphide, when a coating of insoluble lead stflphide is formed, on or through which the paraffin-oil has still less action than on or through the lead sulphate. The impregnation of the oil, however, still goes on, though in a minimum degree.

The paraffin-oil employed in the principal trials was of excellent quality, and was free from acid and alkali. The action, therefore, of the oil upon the metals was not due to the presence of any impurity in the oil In other experiments made with different samples of paraffin-oils upon the metal lead, it was found that the power of action differed materially in the various oils, but such difference in degree of action was not traceable to impurities in the oils. It is probable, however, that the various proportions of the hydrocarbons present may have an influence in aiding or arresting the action of the oil upon the metal. (Dr. Stevenson Macadam.)

Some time since, Chevreul studied the effect produced upon the drying-oils by different metals. He found that under certain circumstances metals exerted an influence upon the oxidation of the oils; for example, linseed-oil, when spread upon a sheet of lead, dried immediately. Livache believed that the metals would act more energetically if in the fine state of division in which they are obtained by precipitation from solution, instead of using only surfaces of sheets of metal. He tried the effect of tin, copper, and lead on the oils, but only the last-named exerted any considerable action. The lead employed in the experiments was obtained by precipitation with strips of zinc from the solution of a lead salt; it was quickly washed with water, then with alcohol and ether, and finally dried in vacuo. If this lead is moistened with a certain quantity of oil, and then exposed to the air, in a short time an increase of weight is observed, and the more drying the oil the greater this increase. When raw linseed-oil is treated in this way, the increase of weight attained its maximum in 36 hours, while the same -oil, if merely exposed to the.air alone, requires several months to reach this state. A solid but elastic substance is formed, like boiled linseed-oil dried in the air.

Experiments made with different oils show that the increase of weight is nearly the same as that of their fatty acids when exposed to the air for a few months:-