Coloured mixes fashioned on the above type may be made up by replacing carbon black by a light mineral and a suitable pigment or dye. Non-bloom browns, greens, crimson, red, etc., can readily be made. Naturally the smoked sheet should be replaced by pale crepe.

Non-Bloom Black (Heels, Tiling, etc.). - Another mix, somewhat heavier than that described above, but yielding a high-grade tough, non-bloom black, suitable for heels, tiling, and the like, is as follows :-

Smoked Sheet ;.... 200

Zinc Oxide ........180

Light Mag. Carbonate 40

Carbon Black ........ 30

Sulphur ;.... .... 4

Z. Suparac .... 4 to 16

It will be noted that a very wide range of accelerator is allowed in the above. For many purposes 4 parts may be ample, but with a slow curing rubber the maximum effect may not be attainable at even 20 minutes at 50 lbs. By increasing the sulphur to, say, 6, a good cure will result in about 10 minutes at 50 lbs., but this may not be absolutely non-blooming. With 8 parts " non-blooming " is practically certain, and a good tough cure results at 10 to 15 minutes. By increasing above 8 the time may be further shortened and s still stronger product obtained. These particulars are given, inasmuch as the actual quantity of accelerator to be used will depend upon practicable costing, whether " non-bloom " is required, degree of toughness, and the like. This mix, in this regard, is an excellent illustration of the many parts which may be played by the super-accelerator.

Stopper Mixings

Black Stoppers :-

Smoked Sheet ;.... 200

Zinc Oxide .... .... 15

Velvet [Slack ........ 5

Litharge ;.... .... 5

Sulphur ;.... .... 4

Z. Suparac .... .... 8

Cure

10 minutes at 50 lbs.

Notes

If "non-bloom " is not required, the Suparac may be reduced to 6 or even 4 parts, and sulphur increased up to 6 parts. To cheapen this mix, barytes or catalpo (colloidal clay), or French chalk may be added, according to gravity and other commercial requirements. For "chemical " stoppers the mix as it stands is very highly recommended.

White Stoppers

-

Pale Crepe ........200

Zinc Oxide .... .... 5

Titanium White ... 25 Sulphur ;.... .... 5

Z. Suparac .... .... 8

Notes

The cure of this white stopper is 10 minutes at 50 lbs. As with the preceding black stopper, the sulphur may be increased, Suparac decreased, and fillers added, as required, but this white as it stands, as well as the corresponding black, are extremely resistant to the action of chemicals, and do not harden even after many months' continual use in contact with most corrosive liquids and vapours. It is believed that chemi cal laboratories (universities, col leges, factories) would readily pay the slight extra cost involved in the production of stoppers of this class, as compared with the cheaper (and generally most unsatislactory) varieties so common in the trade.

Bed Slopcers

A good red may by obtained by replacing the titanium white in the above " white" bv means of suitable quantities of vermilion and an inert filler (say barytes or china clay), according to shade and gravity required-Tiling White Extra Heat Resisting.-The following gives a very good, strong white at a cure of 20-40 minutes at 40 lbs. (according to thickness and curing conditions ; in the press for, say Jin. material 40 minutes is ample). A remarkable property of this mix is that it will stand prolonged heating with out hardening or deterioration. Thus, in one experiment the goods were heated for 3 hours at 50 lbs. without noticeablv affecting the tensiles or pliability. The mix is as follows :-

Pale Crepe ........200

Zinc Oxide .... .... 50

Titanium White .... 100

Sulphur ;.... .... 4

Z. Suparac .... .... 8

Note

Where resistance to heat or " non-bloom " are not of importance, the sulphur can be increased and accelerator decreased (say. 6 sulphur and 4-6 accelerator)

Moulded Hot Water Bottle Mix

A high-grade bottle mix is as follows :-

Pale Crepe ....... ;136

(iolden Antimony* .... ;20

Crimson Antimony* ;14

Vermilion .... .... ;4

Zinc Oxide .... ;8

French Chalk ........ ;10

Miica ............ ;30

* The antimonies contain 16 per cent, free sulphur.

Suparac -4 to 6.

Cu Re (Press)

30 m in u tes a t 40 lbs.

Ebonite Mixings

The following are typical examples of high-grade ebonites : -

The cure for the above is (for lin. to (in. rod) 20 minutes' rise plus 60 minutes at 50 lbs. A longer "step " rise to 10 lbs. and corresponding cure may be preferable in some cases. For cheaper grades "dust "may be replaced wholly or in part by colloidal clay ("Catalpo ") and the Standard "Suparac " replaced by an equal weight of "Z " cures being suitably adjusted. litharge up to 2 per cent, is advisable where the master-batch method is not used.

Mixings containing Brown "Sub."

- Mixes, made up as follows, cure excellently in 10-15 minutes at 50 lbs. (press) :-

The above mix may (when there is no special objection) be cheapened by raising the sulphur, say, to 6-8, and reducing the accelerator to 6 to 4.

With regard to the above mixes generally, most of them are of comparatively high grade, but if it is required to cheapen them, this can be readily effected by introducing appropriate (inert) minerals, brown sub., alkali-reclaim, etc. .4s softeners, where requisite, you can use stearic acid, Stockholm tar pilch, brown sub., mineral rubber.

"Standard " Suparac

When it is desired to reduce the mineral matter to a minimum, or when a very intense acceleration is wanted, " Standard " Suparac should be used instead of the " Z " grade.

With "Standard " it is preferable to use a weight of zinc oxide to equal that of the accelerator. (Midland Tar Distillers Ltd.)

Rubber-Artificial

Among the many formulae are :-

(1) ;Linseed oil 2 lbs., cottonseed oil 1 lb., petroleum 1 lb., raw turpentine 1/2 lb., liquid coal tar 3 lbs., peanut oil 1 lb., spirits of turpentine 1 lb., sulphur 4 lbs. Mix well, boil for 35 minutes.

(2) ;Linseed oil 2 lbs., cottonseed oil 1 lb., petroleum 2 lbs., raw turpentine 2 lbs., sulphur 2 lbs. Mix well and boil for 2 hours.