the mass of bones until the faintest film of solvent only is seen separating from the condensed water running into the receiver.

The operation, which has taken from eleven to twelve hours, is finished with the closing of all valves and the removal of the manhole doors to facilitate the escaping steam, and to dry the bones, which are then raked out and conveyed by a railway to the cleanser, and from thence to the glue-boiling house. The degreased bones are in a dry condition, free from smell, and retain on an average only 2 per cent. of fat on being withdrawn from the extractors.

In the meantime, the crude fat is receiving attention in the mont-jus. As it leaves the extractors, it retains a portion of the solvent along with dirt and mineral matter, and it is the object of the second distillation to recover this solvent, the other impurities being removed by a subsequent washing which the fat receives.

The mont-jus T is a still heated by the steam pipe V, and is provided with an outlet pipe O, through which are conveyed the solvent vapours to the main pipe of the condensers. On the mass being brought to the boil, the solvent vapours pass freely over and the heat is continued for about two hours, at the end of which time the fat will retain only a faint smell of the solvent, while the film at the receiver will be but barely visible. These results being attained, the main valve is closed and hot water run in through the pipe Q from the cistern P, heated by a connection from the main steam pipe. As the water flows in the fat is floated through the pipe R, the valve of which has been opened, to the washer S, where it undergoes a boiling with water for three hours, the aim being to deposit the dirt and mineral matter and leave a clean fat, which is floated off by means of hot water, the stream of fat being distributed by pipes into a number of casks conveniently placed for filling.

Analyses of Finished Fat.-The following analyses, by the author, represent the composition of the finished fat:

Fat extracted by solvents is darker in colour than that produced by boiling or steaming the bones. The colour, however, can be brought up to a good white by bleaching. It is bought on a basis of 98 per cent., a limit of 2 per cent. being allowed for moisture and other impurities. In order to improve the colour of the fatty and gelatinous matter of the bone, some manufacturers, prior to the benzene treatment, bleach the raw material by immersion in a very dilute solution of sulphurous acid. As presently carried out, the degreasing by solvents and the subsequent degelatinisation of the bones after cleansing, form three operations which are costly to the manufacturer, from the frequent handling of the material and the heavy consumption of steam. To reduce this cost attempts have been made to combine the degreasing and degelatinising of the bones in one operation, and thus dispense with the cleansing process. To this end, tetrachloride of carbon, and also the mixed vapours of benzene and steam acting in a battery of extractors working together, have been suggested. Unfortunately, while the extraction of fat is up to the standard, the resulting gelatinous liquor fails to yield a clear and bright glue.

The process of cleansing has for its object the removal of loosely adhering dirt and fleshy matter, and is carried out in a

large cylindrical drum A (fig. 5), measuring 14 feet in length by 7 feet in diameter, horizontally working on a central shaft. The drum is open at both ends, and covered with a stout wire gauze. At the charging end B the degreased bones are fed through a hopper C, and as the drum slowly revolves they undergo a polishing action by friction, the detached mineral and organic matter falling through the meshes of the wire gauze into a chamber D below. From

the discharging end E the cleansed bones are conveyed to the acid steeping vats for gelatine making, or to the glue house. As is seen from the following analyses by the author,

the coarse meal passing through the meshes of the cleanser contains a high percentage of nitrogen, which, however, is not wholly derived from the bone itself, but partly has its origin in the hair of skins connected to the bone, or passing

in a loose state into the extractor. In the former condition only is the nitrogen of a glue-forming nature, and to recover it the coarse meal is passed through a smaller revolving cleanser, covered with a 30-mesh wire. Here fully half the weight is separated, and as it leaves the discharging end of the cleanser is bagged and passed on to the glue house for further treatment.

The dust or flour falling through the netting is sold as a low-grade bone meal, or used in the mixings of the manure house.

The following yields are taken from the returns of several runnings made with raw bones:

When in a condition ready for glue-making the cleansed bones contain 5 to 6 per cent. of glue-forming nitrogen and 58 to 62 per cent. of phosphate of lime.

CHAPTER III.-GLUE (continued).

As previously remarked, glue does not exist ready formed in nature, but is the product of heat on nitrogenous animal tissues, and this work, as carried on in the boiling house, requires the exercise of much knowledge and skill on the part of those engaged in it. The operations of the boiling house may be divided into (a) Conversion of the tissues into a glue liquor by steam and water; (b) clarification; (c) concentration; (d) bleaching.

With steam and water alternately playing on the bones, or by the action of direct steam, the extraction is made in large boilers, built of steel plates 3 in. thick and holding from three to five tons according to the method used. By the adoption of the first, the boilers AA are worked in couples as seen in elevation, fig. 6. The glue liquors are, however, bulky, and low in strength, which renders them troublesome in clarification and costly in concentration. For these reasons many manufacturers prefer the second or direct steam method as a more economical process of extraction. In fig. 7 is represented a section of a boiling house working with direct steam and illustrating the arrangement of boilers, clarifiers, etc, the ground and first floors being shown in part in the plan, fig. 8. Each boiler A is fitted with a false bottom B and provided with charging and discharging man