By determining the volume of the wet skin in the volumenometer, and the per cent. of water on drying the skin, the calculated densities were-- Limed skin 1·438 Puered " 1·300 II. Correcting for ash and fat, the dry ash-free skins had the densities-- Limed skin 1·397 Puered " 1·335 III. The density of the wet limed skin was 1·063, but the density calculated from the results (I.) above is 1·0475; from this, it is evident the fibres of the swollen limed skin undergo compression on swelling, or that the water contained in them is in a state of compression, in the same way as gelatin swollen with water occupies a less volume than the sum of the volumes of gelatin and water. Lüdeking[50] found for 10 per cent. gelatin jelly δ = 1·069; δ calculated was 1·041. He attributed the whole of the compression to the water, so that 1 c.c. of water in a 10 per cent. gelatin jelly occupied a volume of 0·96069 c.c. See also par. 4 p. 68. [50] Wiedemann’s Annal d. Physik, xxxv. p. 352 (1888). It may be of interest to give the figures used in the preceding lines in tabular form. ---------------------------------------+----------+------------ |Limed skin|Puered skin ---------------------------------------+----------+------------ Density of wet skin | 1·063 | 1·053 Per cent. of water found | 80·63 | 78·2 " " calculated | 79·50 | 79·9 " of ash on wet skin | 1·71 | 1·17 " of fat " " | 0·151 | 2·6 Density of dry ash-free skin substance | 1·3970 | 1·3356 ---------------------------------------+----------+------------ In addition to the diminution of the density of the skin by puering, the increase of fat is very marked. The percentage of water referred to the wet skin may be calculated from the formula ((_v__{2} - _v__{1})/(1 - _v__{1})) x 100 where _v__{1} = specific volume of the dry skin. _v__{2} = specific volume of the wet skin. The specific volume of the dry skin (_v__{1}) may be calculated from the specific volume of the wet skin (_v__{2}), the percentage of water (_w_) being known by the following formula:-- _v__{1} = (_v__{2} - (_w_/100))/(1 - (_w_/100)), and by comparing the volume thus obtained with the volume determined by direct experiment, the amount of contraction is ascertained. In the case we have been considering (viz. limed skin with 80 per cent. water) _v__{2} calculated = 0·955 _v__{2} found = 0·941 The specific volume of the dry skin _v__{1} calculated = 0·6955 _v__{1} found = 0·8112