The Optical Magic Lantern Journal (October 1901)

The (Optical Magic Lantern Journal and Photographic Enlarger. 65 a proper definition. In considering the raw material, india-rubber, we must first explain that there are nearly 100 different descriptions of raw rubber which come on the market, and all these descriptions have a variety of grades which depend upon the purity, the state of preservation effected by the cure, the damage (if any) during transit, and a host of other circumstances; so that at hardly any time in the early history can rubber be termed absolutely pure, even before it arrives at the rubber factory. During the progress of manufacture certain colouring matters, vulcanising agents, and other substances are added for special purposes, so that, although the rubber may be as nearly pure as is possible, the article, whatever it may be, cannot be called pure rubber, because there is always a certain percentage of other matter contained therein, each of which has its own particular function to fulfil; and even as a brick-built house is not only built of bricks, but timber, mortar, iron and stone, so are rubber goods composed of rubber and other elements. Again, some buyers have heard that Para rubber is the best, and insist upon their goods being made of pure Para! As we have already stated, there are many grades of Para, but while one is suitable for the manufacture of certain goods, it would not answer for another ; hence the buyer must to some extent depend upon the experience of the manufacturer to supply him with material suited to the purpose. We often get consulted as to the quality of goods which were bought as so and so, but we are often compelled to smile at the ignorance of the buyer, of knowledge, has endeavoured to make what he considers a splendid bargain. It is not only among small buyers that this sort of thing exists. We know of cases where Government contracts have been placed for india-rubber goods, in the manufacture of which it is specifically stated only pure Para is to be used, while it is obvious to all who know what things should be, that it would be impossible to carry out to the letter the conditions of the contract. who, with his small modicum | It is tendered for on the understanding that the | with—those placing the contract knowing that they cannot enforce the conditions, and the ‘tenderer, when he obtains the contract, simply uses what suits him best, provided that the finished article sufficiently conforms to the requirements to pass muster before the authority whose duty it is to vouch for the quality of the goods when supplied.” ' and is grooved as shown ; grinding machine are shown in Fig. II. | wooden framework of the machine, is glued to JNIVE grinding is by no means an unfamiliar occupation. We are all acquainted with the gentleman who ‘s_ obligingly comes to our very doors 5 with his machine to put into proper order our blunted scissors and knives. There is the well-known knife grinder who sets his machine up in a sel country village, to whom the rustics go with their various cutting implements. His machine is of a somewhat more substantial order and solid appearance than his itinerant brother’s, as it is called upon to do much heavier work. The present slide gives a representation of him engaged in grinding ascythe. For the purposes of construction, a wooden framework of simple design and two fixed glasses are used; one being employed merely as a protective or cover lass. : The various parts of the grinder and his K, the the inner surface of the fixed glass, upon which it is intended that the various parts should be mounted, as shown in Fig. I. The body (8, Fig. IT.) ‘of the grinder is cut out of wood, and corditions will not be expected to be complied | glued to the fixed glass as shown in Fig. I. The grindstone (F, Fig. II.) is made of wood, in the sectional drawing by its side. It is also furnished with a small projecting pin, and it is attached to the framework x by means of a screw (H, Fig. I.) upon which it is free to revolve. Tne lower part of the grinder’s leg and the treadle of the machine are in one piece (E,