August, 1925 INDCSTRIRL A S D ELTGI,VEERISG CHEMISTRY 829

Variation of Strength and Stretch over the Area of Calf Leather'

By John Arthur Wilson

A. F. GALLUN & SONS Co , MILWAUKEE, WIS.

HE strength of leather varies so widely in different parts of the skin as to make recorded values meaning- less if the location of the test piece is not indicated.

As a preliminary to some work on the life of leather as a function of several variable factors, tests were made of the strength and stretch of every part of a number of calf skins. The results are valuable in suggesting to the experimenter how to cut leather strips for tests involving strength andstretch and how to interpret his results. They are also a valuable guide in the ordinary cutting of leather where strength and stretch are important factors. They are presented in this paper as a needed addition to the literature.

I n making these measurements, it was appreciated from work already done that the results depended not only upon the location of the test pieces, but also upon the extent to which

T

1 Presented under the title "Detailed Studies of the Strength and Stretch of Leathers" before the Division of Leather and Gelatin Chemistry at the 69th Meeting of the American Chemical Society, Baltimore, Md., April 6 to 10, 1925.

1 20 15 10 5 0 5 10 15 20

left r l g t Inches from Backbone

Figure 1-Variations in Strength and Resistance to Stretch of Strips Cut Parallel Calf Leather from Different Parts of the Skin.

to Line of Backbone

the skin was split or shaved, the water content, oil content,2 etc. For the first tests four calf skins were selected, two vegetable-tanned and two chrome-tanned. Every effort was made to select skins that could be considered representa- tive of the general leathers of the market. Each was kept for a week or more a t a relative humidity of 50 per cent and then cut into as many strips as possible with a die 15.24 X 2.54 cm. (6 X 1 inches). With one skin of each kind, all strips were cut with their lengths parallel to the line of direction of the backbone and with the others a t right angles to the backbone line.

The tests were made on a Scott machine equipped with a device for recording the stretch as a function of the load. The jaws were set 10.16 cm. (4 inches) apart. Thickness was measured with a gage reading to 0.001 cm.

It will suffice here to give detailed results only for the vegetable-tanned leather, as these were found to be typical. The analyses of these two skins follow:

-PER CENT- Skin 1 Skin 2

Water Protein (N X 5.62) Fa t (chloroform extract) Water-soluble matter Combined tannin Ash Sulfuric acid Average thickness (millimeters)

1 4 . 0 1 3 . 9 40.1 4 1 . 5 1 3 . 4 1 2 . 1 8 . 9 8 . 5

2 2 . 4 2 3 . 5 0 . 8 0 . 6 0 . 3 0 . 6 1 .03 1 . 2 0

* Wilson'and Gallun, THIS JOURNAL, 16, 1147 (1924).

i I I

25 20 15 10 5 0 5 10 15 20 25 head ta i l

Inches from Midline Figure 2-Variations in Strength and Resistance to Stretch of

Strips Cut at Calf Leather from Different Parts of the Skin. Right Angles to Line of Backbone

830 INDUSTRIAL d.VD ENGINEERISG CHEMISTRY Yol. 17, No. 8

T e n s i 1 e strength less than 170 kg 1-1 Stretch greate; than 60 per cent [=I Tensile strength 170 to 260 kg.

Stretch 60 to 26 per cent

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 de- viation in stretch. The per- centage stretch in Figure 2 is plotted on a larger scale than in Figure 1 because of the lesser deviation.

On an average, the chrome

(Tensile strength given in kg. per sq. cm ) (Percentage stretch measured under load of 225 kg. per sq . cm.) Figure 3-Chart Showing Variations in Strength and Resistance Ir to Stretch of Calf Leather from Different Parts of the Skin

Tensile strength 260 to

Stretch 26 to 20 per cent 350 kg.

cent

skins were a little weaker and showed a little more tendency to stretch, but the total differ- ence between the chrome and vegetable-tanned skins was too small to warrant giving the re- sults 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 pre- pared. It shows how the strength and tendency to stretch are distributed over the area of what may be con- sidered 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 & FORBES C O . , CAMDEN, N. J.

M AKY forms of continuous extraction apparatus have been described, among recent ones being those of Sando12 Lloyd,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 appara- tus.

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 one- third 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 to

1 Received May 4, 1925. * THIS JOURNAL, 16, 1123 (1924). 8 Am. J . Pharm., 97, 42 (1925J. 4 THIS JOURNAL, 12, 173 (1920).

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 sol- vent is complete, valve H or H’, connected with the recently emptied percolator, is closed. When ether or other extra- hazardous 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 sol- vent which the writers have usually employed. KO fire 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 com- position of its link is adjusted to give the desired melting