CHAPTER IV.

MANUFACTURE OF SKIN GLUE.

Classification of operations; Definition of crude glue; Derivation of the bulk of this stock 43

Cooking or boiling glue-stock; Boiler for this purpose, and manner of using it 44

Duration of boiling 45

Mode of ascertaining the progress of the operation; Convenient apparatus for glue-boiling with water, described and illustrated 46

Extracting the glue stock by the use of steam 47

Boiler for this purpose, described and illustrated; Use of open-jacketed pans heated by steam, described and illustrated 49

Process of cooking as described by Mr. Thomas Lambert; Terne’s glue boiler, described and illustrated 51

Clarifying the glue-liquor 52

Distinction between clearness and color; Clarifying vats; Prevention of putrefaction of the liquor 53

Use of alum and other chemicals for clarifying; Freeing the liquor from coloring substances 54

Use of animal charcoal for this purpose; Bleaching the raw materials previous to boiling them to glue; Use of chloride of lime or of sulphurous acid for this purpose 55

Forming or moulding the glue; Moulds for this purpose 56

Detaching the glue from the sides of the moulding boxes; Cutting the cubes of glue into commercial cakes or sheets; On what the shape of the cakes depends 57

Use of stone-slabs in place of cooling boxes; Use of glass or zinc plates for liquors which in gelatinizing do not become very solid 58

Tools for cutting the jelly into cakes, described and illustrated 59

Machine for slicing and spreading glue-jelly preparatory to drying invented by Mr. J. Schneible, described and illustrated 60

Cutting apparatus patented by M. Devoulx, described and illustrated 62

Drying the cakes of glue; Drying in the open air; Mode of conducting the operation in a drying room 64

Size of the drying room; Circulation and change of air in the drying room 65

Nets and frames for drying the glue; Objections to twine netting 66

Metallic netting and its advantages; Regulation of the temperature of the drying room; Means of promoting the dryness of the air 67

Use of long drying galleries; Apparatus for drying glue, invented by W. A. Hoeveller, described and illustrated 68

Modern drying house, described and illustrated 71

Method to accelerate the drying of glue, proposed by Fleck 72

Mode of giving the dry cakes a good lustrous appearance 73