The statements which have been recently made in the daily papers as to the effects produced by the use of primary batteries in lighting railway carriages have brought many queries, not a few from persons who appear to imagine that the cost of lighting by that means is measured by the first cost of the battery and the lamps. Most schoolboys have nowadays learned the simple lesson that out of nothing, nothing comes; but judging by some of the paragraphs in daily papers, it is perhaps excusable that not a few of our querists should imagine that something remarkably cheap has been discovered, and that they can have the electric 5 light at a merely nominal cost. We have recently pointed out, not once merely, but several times, that an electric light obtained from any known battery is really expensive as compared with the same amount of illumination obtained from gas or other cheap source of light, and that there is no hope of reducing the expense until someone discovers a battery the decomposition of the elements of which will produce a substance or substances which shall be worth at least as much as the raw materials themselves.

We have, from time to time, described cells or battery arrangements, patented and otherwise, the inventors of which thought they had made one step towards the desired goal; but at present, notwithstanding all the puffing, we are unacquainted with any battery which, all things considered, is cheaper than the well-known combination of zinc and carbon excited by dilute sulphuric acid and bichromate of potash or nitric acid. For bells, telephones, and telegraphs, electro-metallurgy and medical purposes, other arrangements are more suitable; but in the case of electric lighting and electro-motors, a constant and ample supply of energy to the full capacity of the battery is required, and at present we have not found a cheaper metal to oxidise or consume than zinc. This is an old tale. It must Le quite 40 years since Staite took out a patent in which the commercial value of the residual products was mentioned, and latterly we have had several inventors taking up the old idea, without, however, demonstrating by actual receipts that they obtained any return worth mentioning for the zinc and sulphuric acid expended.

Probably if primary batteries came to be used on a very large scale indeed, a sufficient quantity of residual products might be obtained to find a ready sale; but it is extremely doubtful whether more than a fraction of the prime cost would be recouped, unless the battery can be induced to manufacture some unknown and really valuable substance whilst giving out current. In one of the new batteries, Which is, we believe, working very well on several railways, lighting carriages with lamps of 5 to 10 candle-power, zinc and carbon form the two elements, and the battery is excited by a composition named "oxidone," the exact nature of which is kept secret until the patents are completed. The working cost of this battery is stated to be as low as 1/8 d. per hour for each 5-candle lamp, and a battery of 16 cells will supply 18 lamps and can be charged for 40 hours - that is, the battery can be used for 10 hours on each of 4 days without needing to be recharged. Taking batteries as we know them in practice, such a result as that must be regarded as very good indeed; but if the cost has been arrived at by allowing for the sale of the residual products, it will at once be seen that the battery is not so cheap as a good steam-engine and dynamo, for when current is obtained by the oxidation of zinc the cost is about 9 times greater than when a machine is used, and the source of the energy is coal at about 205. a ton.

Sprague worked out this little sum for the benefit of all whom it concerns some years ago, and he found that taking the expense of the battery as only 4rf. per lb. of zinc, the cost of a horse-power for 24 hours was 25s., whereas the same amount of energy could be obtained from a common steam-engine and coal at 20s. for 10.29d. Even if we suppose the residual products of any battery in which zinc is employed return 2d. for every lb. consumed - and no one has supposed that possible amongst the most sanguine inventors - it will be seen that the common steam-engine has still the advantage as a motive power. Electrical machines have been considerably improved since Joule calculated that 75 lb. of zinc would be necessary for one to maintain 1 h.p. for 24 hours; but so have steam-engines, and, therefore, we are brought back to the simple datum that the oxidation of zinc can produce so much and no more energy, and that unless some one can be found to pay a high price for sulphate of zinc there is no chance of any of the well-knewn cells in which it is consumed becoming a cheap source of electric light.

It seems abundantly clear, from a number of experiments, that the most that can be expected from the best steam-engines and dynamos is 200 candles of incandescent lighting per h.p.; and as it is also tolerably apparent that 2 lb. of zinc are necessary to obtain the same quantity of energy, we have 6d. as compared with \d. as the relative cost of the two sources of energy for electric lighting. It is not impossible that these figures are too favourable to the battery, for Sprague says that the cost of an equivolt of energy by a common steam-engine, is only .00112d., while by a Daniell's battery it is .0541d. There is this to be said, however, that even if the cost of working a 20-candle lamp is as much as 1/4d. per hour, there are many persons who would prefer it to gas or any other illuminant; and if the new batteries can be made to produce a really useful substance as a residual, the trouble and attention they may entail will not stand in the way of their adoption. So far as we know, a 20-candle light cannot be maintained at a cost of 1/2d. per hour, even when the zinc and the acid can be purchased in quantities at the lowest price; but if a battery is in existence which will yield such results, it is a pity those who own it do not make it known, for it is certain they would have a very wide sale, provided they could guarantee its performance.