Yol. 17, No. 8
INDUSTRIAL d.VD ENGINEERISG CHEMISTRY
830
Tensile strength 260 to 350 kg. Stretch 26 to 20 per cent
T e n s i 1 e strength less than 170 kg Stretch greate; than 60 per cent Tensile strength 170 to 260 kg. Stretch 60 to 26 per cent
1-1
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The strips from Skin 1 were cut parallel to the line of the backbone, and the results of the tests are shown in Figure 1. The strips from Skin 2 were cut at right angles to the line of the backbone, and the results are shown in Figure 2. Because of the irregular shape of the skins, it was not possible to include the loosest parts of the flanks in the second series, which explains the lesser deviation in stretch. The percentage stretch in Figure 2 is plotted on a larger scale than in Figure 1because of the lesser deviation. On an average, the chrome
cent
(Tensile strength given in kg. per sq. cm ) (Percentage stretch measured under load of 225 kg. per s q . cm.) Figure 3-Chart Showing Variations in Strength a n d Resistance Ir to Stretch of Calf Leather from Different Parts of t h e Skin
skins were a little weaker and showed a little more tendency to stretch, but the total difference between the chrome and vegetable-tanned skins was too small to warrant giving the results separately. The work was carried further by making numerous tests on many types of skin. From all of the available data the chart shown in Figure 3 was prepared. It shows how the strength and tendency to stretch are distributed over the area of what may be considered a good average calf skin in condition ready for cutting into shoes.
Continuous Extraction Apparatus’ By Percy A. Houseman and Clement K. Swift LABORATORY O F hIAC.%NDREWS
M
AKY forms of continuous extraction apparatus have been described, among recent ones being those of Sando12Lloyd,3 and of the present authors.‘ The authors have now modified their extraction apparatus so that i t contains a number of features, notably safety devices, which are embodied in no other continuous extraction apparatus. Apparatus and Operation
A and A’ are jacketed, cylindrical copper percolators, 150 em. long, 20 cm. diameter of percolator, and 26 cm. outside diameter. Each percolator is fitted with a cage made of sheet iron and provided with a perforated bottom. The cage holds about 10 kg. of ground drugs or plant materials and about twice that amount of dried extracts. B is a 22-liter, short-neck Pyrex flask containing the solvent and immersed in a paraffin bath. Increased safety is achieved by the use of a copper receiver instead of the glass flask. Such a receiver is provided with sight glasses placed a t onethird and two-thirds of the height of the receiver. The copper receiver also has an outlet passing through the bottom of the paraffin bath. A valve is attached to this outlet andserves to remove the extracted material after the solvent has been distilled off and the residue dissolved in a suitable solvent. The paraffin in the bath is heated by an electrical heater made of 17-gage monel metal wire. The vapor of the solvent passes up the pipe C (36 mm. i. d.), enters the top of the percolator, and is condensed by the coil condenser, D. The solvent drops back a t its boiling point onto the material to be extracted. The extract siphons continuously from the bottom of the percolator, returning t o 1
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8 4
Received May 4, 1925. THISJOURNAL, 16, 1123 (1924). A m . J . Pharm., 97, 42 (1925J. THISJOURNAL, 12, 173 (1920).
& FORBES CO.,
CAMDEN,
N. J.
the flask, B, through the constant-level siphon tube, E (16 mm. i. d.). When the extraction is finished the heating is interrupted. The percolator head carrying the condenser is transferred from the old to the new percolator and the solid head put on the old percolator. The solvent remaining on the extracted material is transformed to the newly charged percolator by means of compressed air or carbon dioxide admitted a t I . Before making the transfer, valves F , F’, and G are closed, and valves H , H‘, and M opened. At the moment the transfer of solvent is complete, valve H or H’, connected with the recently emptied percolator, is closed. When ether or other extrahazardous solvent is used, carbon dioxide is preferred for transferring, in order to minimize the danger of explosion should a leak develop. After opening valves F , F’, and G, steam is turned into the jacket of the old percolator in order to recover the solvent absorbed by the extracted material. hleanwhile, the new percolator is set in operation, since no condensation of solvent will occur in the old percolator while it is hot. kt appropriate times the siphon line to the flask is closed and the solvent distilled off from the extract into the percolator. h fresh flask is then put into the paraffin bath, and the extract in the old flask is worked up as may be necessary. The apparatus runs day and night, having been applied to the extraction of a variety of materials. Ether is the solvent which the writers have usually employed. KOfire or explosion has occurred during the several years the apparatus has been in use, and the loss of ether is negligible. Safety Devices
Overheating of the paraffin bath melts the fusible link, J , and causes the current to be cut off from the heater. The composition of its link is adjusted to give the desired melting
August, 1926
I.\TDC'STRIA4LA S D EXGIXEERISG CHEMISTRY
A'
831
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point. For most purposes a fusible link melting a t 140' C. has been found suitable, but the sensitivity of the extract must be considered as well as the safeguarding of the paraffin from overheating. In case the paraffin should solidify after the melting of the fuse, an external switch is provided to shunt the fuse circuit temporarily and permit the paraffin to be re-
melted. If the pressure of the condenser water falls below a predetermined limit, connection is made to the relay K and the current to the heater is cut off. Resumption of normal water supply causes the heating to be renewed. The bottle L contains mercury through which excessive pressure of uncondensed solvent would be relieved.
