Purified rape oil is that of which the use is the most general. Next to olive oil and wax, it affords the greatest heat, and the least smoke. But, in a word, as in the working of glass, the operator has more need of a bright flame without smoke, than of a high temperature, any combustible may be employed which is capable of furnishing a flame possessing these two qualities. The vegetable oils thicken, and suffer alterations more or less sensible, when they are long exposed to the action of the air. They should be chosen very limpid, and they may be preserved in that state by being enclosed in bottles, which should be kept quite full and well corked.
The Wicks.—There has never been any substance so generally used for wicks as cotton; some glass-blowers, indeed, have employed wicks of asbestus, but without deriving from them the advantages which might have been expected; the greater number, therefore, keep to cotton.
But it has been observed that cotton which has been for some time exposed to the air no longer possesses the good properties for which glass-blowers esteem it. The alteration of the cotton is probably brought about by the dust and water which the air always holds in suspension. Such cotton burns badly, forms a bulky coal, and permits with much difficulty the capillary ascension of the liquid which serves to support the flame; so that it is impossible to obtain a good fire, and necessary to be incessantly occupied in snuffing the wick. Cotton is equally subject to alteration when lying in the lamp, even though impregnated with oil. You should avoid making use of wicks that are too old. When you foresee that you will remain a long time without having occasion to employ the lamp, pour the oil into a bottle, which can be corked up, and let the wick be destroyed, previously squeezing from it the oil which it contains.
It is indispensable to make use of none but new and good cotton; it should be clean, soft, fine, and not twisted. It is best to preserve it in boxes, after having folded it in many double papers, to exclude dust and moisture. When you wish to make wicks, take a skein of cotton and cut it into four or six pieces, dispose them side by side in such a manner as to make a bundle, more or less thick, and eight or ten inches in length; pass a large comb lightly through the bundle, to lay the threads even, and tie it gently at each end, to keep the threads from getting entangled.
Relation between the diameters of the beaks of the blowpipe, and the wicks of the lamp.—We believe that we cannot place better than here a few observations respecting the size of the opening in the beak of the blowpipe, considered in relation to the size of the wick of the lamp. These observations will probably be superfluous to those who are already conversant with the use of the blowpipe; but as every thing is interesting to beginners, who are frequently stopped in their progress by very slight difficulties, and as this Treatise is particularly designed for beginners, we do not hesitate to enter into the minutest details on subjects which we deem interesting.
The point of your blowpipe should be formed in such a manner, that you can fix upon it various little beaks or caps, the orifices in which, always perfectly round, ought to vary in size according to the bulk of the flame upon which you desire to act. You cannot, without this precaution, obtain the maximum of heat which the combustion of the oil is capable of affording. This employment of little moveable caps offers the facility of establishing a current of air, greater or smaller, according to the object you wish to effect; above all, it allows you to clean with ease the cavity or orifice of the beak, as often as it may be necessary.
These caps can be made of different materials. It is most advisable to have them made of copper or brass; those which are formed of tin plate (white iron), and which are commonly used in chemical laboratories, are the worst kind of all. They soon become covered with grease or soot, which either completely closes up the orifices, or, at least, very soon alters the circular form which is necessary to the production of a good fire. Glass caps are less liable to get dirty, and are much cheaper than the above; but, on the other hand, they have the disadvantage of being easily melted. This can to a certain extent be remedied by making the points of very thick glass, and by always keeping them at some distance from the flame. Moreover, as you can make them yourself when you are at leisure, their use is very commodious. If they are to be used with the blowpipe described in this work, they must be fixed in the cork that closes the passage through which the current of air arrives. C c and C´ c ([pl. 1], fig. 19) are two glass beaks, c c are the corks, which can indifferently be adapted to c, in the wooden vice, by which the various parts of the blowpipe are connected when it is in action.
Of whatever material the beak may be made, its orifice must be perfectly round, and the size of the orifice, as we have before observed, must have a relation to the size of the wick which is to be used with it. You can ascertain the diameters of the orifices by inserting into them a little plate of brass, having the form of a long isoceles triangle, such as is represented by [pl. 1], fig. 2. It should be an inch long, the twelfth of an inch wide at one end, and diminish to nothing at the other. When divided into eight equal parts, it will give, at the divisions, the respective proportions of 1, 2, 3, 4, 5, 6, 7 eighths of the diameter at the wide end, as is exemplified by the figure above referred to. We have stated in the following table the relative diameters which long experience has recommended to us, as being adapted to produce the greatest effect; yet it is not to be imagined that these proportions are mathematically correct and indispensable for the obtaining of good results. A sensible difference of effect would be perceived, however, were these proportions departed from in a notable manner.
| Diameter of the wick, in inches. | Diameter of the orifice of the beak, in parts of an inch. | Height of the wick above the surface of the oil, in inches. |
|---|---|---|
| ¼ | 96th | ½ |
| ½ | 48th | ½ |
| 1 | 24th | ¾ |
| 1½ | 16th | 1 |
| 2 | 12th | 1¼ |
It must be mentioned, that this table has been formed from experiments made with a glass-blower’s lamp of the ordinary construction; so that, with the new lamp with the hood, described in this work, it will not be necessary to employ wicks of so great a bulk, nor yet to elevate them so much above the level of the oil, in order to produce the same effect. Hence there will be a very considerable saving in oil.