CHAPTER III.

RAW MATERIALS AND THEIR PREPARATION FOR THE MANUFACTURE OF GLUE.

Principal substances employed for the manufacture of glue; Division of raw materials into groups 16

Animal skin and its constitution 17

Portion of the skin of value for the manufacture of leather and glue; Yield of glue from tannery waste; Influence of the age of the animals from which the skins have been derived upon the quality of the glue 18

Notes in reference to judging glue-stock 19

Liming of waste 20

Precaution and care required when buying glue leather; Arrangements required for the preparation of glue stock; Location of the glue factory; Lime pits; Contrivances for washing the limed stock 21

Washing drums; Pits or vats with proper arrangements for stirring, draining and inspection; Glue stock washer invented by W. A. Hoeveller, described and illustrated 22

Sheds for storing and sorting; Mode of carrying on the work in the factory; Liming; Preparation of milk of lime 26

Importance of the quality of the lime used; Testing the value of a lime by determining the amount of real calcium hydroxide contained in it; Mode of conducting the operation 27

Washing the material after removal from the lime pit; Washing and drying 28

Preservation of the glue-stock by means of carbolic acid; Preparation of carbolic acid solution for this purpose 29

Use of other antiseptics for the purpose of preventing putrefaction; Formaldehyde and boric acid; Classification of the principal varieties of hides and leather for glue-stock 30

Bones and cartilages 31

Constitution of bones; Composition of bone cartilage; Value of bones for the manufacture of glue; Necessity of exercising care in buying bones 32

Sorting the bones; Crushing or grinding the bones 33

Stamping mill for crushing bones, described and illustrated 34

Bone crusher, described and illustrated; Crosskill bone mill, described and illustrated; Sieve for sorting the crushed bones, described and illustrated 36

Lime bath for bones; Treatment of the bones with hydrochloric acid 37

Washing the stock; Use of dilute sulphurous acid in place of hydrochloric acid as suggested by Gerland; Jullion and Pirie’s process for the preparation of gelatine from bones 38

Leather waste; Mechanical manipulation of the waste; Comminution of the waste and use of a rag-engine or hollander for this purpose 39

Various methods of extracting tannin from leather waste 40

Raw materials for fish glue; Difference between isinglass and glue manufactured from entire fishes; Principal points to be observed in the manufacture of fish glue 41

Utilization of scales of large fishes 42