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second expression with the open Anglo- the pressing cages and replacing them, the American press. The finishing presses are work goes on continuously. Further advantages of the same type as the press in which are offered by these presses, in that the cakes the first expression is carried out, and by require no paring, and that great saving of making the press cages removable, the press- press cloths is effected in comparison with the ing operation can be made a practically con- open plate process of the Anglo-American tinuous one. These press cages can either system.
be transported by means of a power-driven 2.-RECOVERY OF THE OILS BY EXTRACTION carriage (Fig. 3) to the finishing presses,
WITH VOLATILE SOLVENTS. or if one preliminary press is combined with The second class of processes for obtaining one or two finishing presses to a battery, the oils and fats from fruits or seeds is represented cages can be conveyed into the adjoining by the so-called “ extracting processes," and is finishing press by a swinging arrangement very largely employed in the extraction of olive (Fig. 4, and Fig. 5), its place being filled im- oil marc and palm kernel oil from palm kernels, mediately by a charged cage, or by a cage rape oil from rape seed, and castor oil from containing finished cakes, so that, with the castor seeds. exception of the time required for withdrawing The solvents employed on a large scale are
almost exclusively petroleum ether and carbon its technical application. Furthermore, its bisulphide ; ordinary ether must be considered physiological effect (similar to that of chloroas altogether outside the range of the solvents form) on the workmen would seem to prevent used on a large scale owing to the considerable its general application. loss of solvent involved, and furthermore on The type of apparatus employed on a large account of the great danger of fire. The same scale depends on the temperature at which the danger attaches, although in a somewhat extraction is carried out. In the case of cold exminor degree, to the employment of petroleum traction (preferable as regards fire insurance), ether. More diminished still is the danger of the seed is placed in a series of closed vessels an inflagration in the case of carbon bisul- through which the solvent percolates on the phide ; as this solvent is heavier than water, counter - current system. The battery of the vapours are less liable to come in contact vessels is so arranged that any one vessel can
with an open flame. Hence, carbon bisulphide i be made the last of the series, ready to disis largely employed for the extraction of oil, charge the extracted meal, and to be refilled notably for the extraction of the marc of olives. with fresh meal, so that, with the exception Still, owing to the physiological effect this of the time required for charging and dissolvent has
upon the workmen, coupled with the charging, the process is practically a condanger caused by the action of impure carbon tinuous one. The solution of extracted oil bisulphide on-iron, which has frequently led to or fat is then transferred to steamconflagrations, the employment of carbon heated still, where the solvent is driven off, bisulphide is restricted.
and recovered by condensing the vapours in An ideal solvent would be carbon tetrachlo- a cooling coil. Thus the same quantity of ride, which is non-inflammable, and has the solvent is used over and over again. The last further advantage of being heavier than water. traces of volatile solvent in the oil or fat are 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 the seed, whilst that portion which leaves the hot.
vessel in form of vapour is condensed in a sepaThe extracting processes in the hot are rate condenser, from which the liquefied solvent carried out in apparatus, the principle of falls back and percolates the seed. Finally, which is illustrated by Fig. 6 (where the when the meal is exhausted, the solvent is condenser is not shown). I further show, in a driven off, and the condensed solvent collected few lantern slides, several types of apparatus in a separate vessel. used on the large scale.
[All these types of apparatus were illustrated The principle involved in more elaborate by means of lantern slides ; finally a series of forms of plant employed on a large scale is slides were exhibited, showing a large rape oil exemplified by the well-know Soxhlet extractor. extracting plant.] The extraction here takes place continuously, In special cases, notably so in the case of with a limited amount of solvent charged once olive oil, a combination of the two processes for all into the apparatus. When the seed is described under the headings 1 and 2 com
mends itself. The combined method consists FIG. 6.
in expressing most of the oil in the cold (for
edible purposes), and then extracting the par. ъ
tially 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."
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 ob
jections can be raised from a sanitary point of deemed completely exhausted, the vessel con- view. The simplest, and as I can testify from taining the seed is disconnected by closing my own experience, very effective method for taps between the oil containing vessel and the obtaining tallow for technical purposes, is to condenser, so that the volatile solvent can throw the rough fat into covered lead-lined be immediately distilled off and and condensed, vessels provided with steam coils, outlet taps, whilst the seed-containing vessel is freed from a trap door for charging the rough fat, and a the last traces of volatile solvent by open steam, wide outlet through which any offensive vapours and emptied and recharged with fresh seed. that may be given off are conducted through More compact still are extractors illustrated closed pipes to the chimney stack, or boiler, or by that form of laboratory apparatus in which fire grate. Hot water is then run on to the fat, the meal-containing vessel is placed inside the and the steam turned on. After heating for a flask charged with the solvent. Thus, in some sufficient length of time the steam is shut off, form of extractors, a basket containing the when the clear melted fat rises to the top. It crushed seed is placed on a support at some can then be drawn off ready for use, or into height above the bottom of the vessel charged another vessel for further purification (refining, with the solvent, so that, on heating, the bleaching). The animal tissue, &c., still con. vapoiis of the solvent pass through and round taining considerable quantities of fat, is boiled
even boil over and run into the flue, whereby volumes of the pungent acroleïn were sent into the atmosphere, a number of apparatus have been designed in which the tallow is melted in closed vessels under pressure. Such vessels termed 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.
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 oft 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,