Puslapio vaizdai
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with an open flame. Hence, carbon bisulphide is largely employed for the extraction of oil, notably for the extraction of the marc of olives. Still, owing to the physiological effect this solvent has upon the workmen, coupled with the danger caused by the action of impure carbon bisulphide on iron, which has frequently led to conflagrations, the employment of carbon bisulphide is restricted.

be made the last of the series, ready to discharge the extracted meal, and to be refilled with fresh meal, so that, with the exception of the time required for charging and discharging, the process is practically a continuous one. The solution of extracted oil or fat is then transferred to a steamheated still, where the solvent is driven off, and recovered by condensing the vapours in a cooling coil. Thus the same quantity of solvent is used over and over again. The last traces of volatile solvent in the oil or fat are

An ideal solvent would be carbon tetrachloride, which is non-inflammable, and has the further advantage of being heavier than water. Its high price has, however, hitherto prevented driven off by a current of open steam whic

is blown through the oil or fat whilst kept hot.

The extracting processes in the hot are carried out in apparatus, the principle of which is illustrated by Fig. 6 (where the condenser is not shown). I further show, in a few lantern slides, several types of apparatus used on the large scale.

The principle involved in more elaborate forms of plant employed on a large scale is exemplified by the well-know Soxhlet extractor. The extraction here takes place continuously, with a limited amount of solvent charged once for all into the apparatus. When the seed is

FIG. 6.

deemed completely exhausted, the vessel containing the seed is disconnected by closing taps between the oil containing vessel and the condenser, so that the volatile solvent can be immediately distilled off and and condensed whilst the seed-containing vessel is freed from the last traces of volatile solvent by open steam, and emptied and recharged with fresh seed. More compact still are extractors illustrated by that form of laboratory apparatus in which the meal-containing vessel is placed inside the flask charged with the solvent. Thus, in some form of extractors, a basket containing the crushed seed is placed on a support at some height above the bottom of the vessel charged with the solvent, so that, on heating, the vapours of the solvent pass through and round

the seed, whilst that portion which leaves the vessel in form of vapour is condensed in a separate condenser, from which the liquefied solvent falls back and percolates the seed. Finally, when the meal is exhausted, the solvent is driven off, and the condensed solvent collected in a separate vessel.

[All these types of apparatus were illustrated by means of lantern slides; finally a series of slides were exhibited, showing a large rape oil extracting plant.]

In special cases, notably so in the case of olive oil, a combination of the two processes described under the headings 1 and 2 commends itself. The combined method consists in expressing most of the oil in the cold (for edible purposes), and then extracting the partially expressed material with volatile solvents, in order to recover the oil left in the press cakes. This combined process is known on the Continent under the name "huilerie mixte."

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Animal oils and fats are usually obtained in a very simple manner by heating those parts of the animals which contain the oil or fat, so as to cause bursting of the fat-containing cells. The older rough and ready methods of heating the adipose tissue over free fire may be considered as almost extinct in this country, but it is still being practised in small establishments on the Continent. The nuisance which follows in the wake of a manufacturing process of this kind has naturally led to stringent regulations on the part of the sanitary authorities.

The rendering of tallow from the "rough fat," as it comes from the slaughterhouses to the rendering establishments is now carried out under such conditions that no serious objections can be raised from a sanitary point of view. The simplest, and as I can testify from my own experience, very effective method for obtaining tallow for technical purposes, is to throw the rough fat into covered lead-lined vessels provided with steam coils, outlet taps, a trap door for charging the rough fat, and a wide outlet through which any offensive vapours that may be given off are conducted through closed pipes to the chimney stack, or boiler, or fire grate. Hot water is then run on to the fat, and the steam turned on. After heating for a sufficient length of time the steam is shut off, when the clear melted fat rises to the top. It can then be drawn off ready for use, or into another vessel for further purification (refining, bleaching). The animal tissue, &c., still containing considerable quantities of fat, is boiled

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even boil over and run into the flue, whereby volumes of the pungent acrolein were sent into the atmosphere, a number of apparatus have been designed in which the tallow is melted in closed vessels under pressure. Such vesselstermed digesters-consist essentially of a vertical boiler provided with a false perforated bottom, and constructed to withstand a pressure of several atmospheres. Live steam is turned into the boiler below the perforated bottom on which the rough fat rests. At the elevated temperature the mass parts readily with its occluded fat, and in a shorter time than by steaming at the ordinary pressure. The first apparatus of this kind was designed by Wilson (Fig. 7); it has served as a prototype for a number of more or less complicated digesters now in use.

Miscellaneous.

MINES AND

FORESTS OF BRITISH
GUIANA.

The Report of the Council of the Institute of Mines and Forests for the year 1903-4 is dated, Georgetown, 18th July, 1904.

Gold.-In submitting to the Institute the Annual Report required by Ordinance 9 of 1890 to be submitted by the Governor and Court of Policy, the Council have to state that for the year July 1st, 1903, to June 30th, 1904, there has been a noticeable falling off in the export of gold from the colony. Customs returns show that for the year 1902-3 there was exported 101,962 ounces of gold of the value of 1,782,747 dols., while the figures for 1903-4 only stand at 99,734 ounces, of the value of 1,585,434 dols,

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