# Page:Popular Science Monthly Volume 70.djvu/262

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THE POPULAR SCIENCE MONTHLY

is shown by the relative heats of combustion to which reference has already been made. So that, at the present time, it is about an even thing between the two sources of power, weight for weight, with the chances good that American ingenuity will develop an alcohol motor superior to the gasoline motor.

Alcohol engines used abroad require a preliminary warming up before they will start. They are sometimes started with gasoline, and sometimes 25 per cent, of gasoline is added to the alcohol to cause it to ignite more readily. This may militate against alcohol as a motive power at the outset, but even now there are to be found in the current literature descriptions of alcohol engines which will start even without this brief preliminary warming.

Numerical data as to the consumption of alcohol per horse power are abundant. On the average, in small motors, the consumption at present may be taken at about one and a half pints of alcohol per brake horse-power hour. Professor Lucke, of Columbia, commissioned by the government, is now engaged upon a series of exhaustive tests of alcohol motors, and his results will be interesting.

Alcohol burns with a non-luminous flame. There are two general methods by which it may be made to furnish light. First, by adding some liquid, like 'benzine,' to it, which causes the flame to become luminous, and second, to utilize the heat to heat a mantle such as the ordinary Auer von Welsbach gas mantle, to incandescence.

A mixture consisting of 65 per cent, to 85 per cent, denatured alcohol and 35 per cent, to 15 per cent, of the distillate from coal tar, boiling between 150° and 160° Centigrade (mainly mesitylene) is on the market in Germany. It is known as 'Plehn's fluid' and burns with a luminous flame.

Before the discovery of mineral oil a mixture of ethyl alcohol and a very pure turpentine which was known as camphene[1] was largely used as an illuminant. It is of course possible to return to the customs of our grandfathers, but unfortunately the price of turpentine has risen enormously in the meanwhile.

On the whole the other method, burning alcohol with a nonluminous flame to heat a mantle on the plan of the Welsbach gaslight, is probably to be preferred to methods for making the flame itself luminous. It may be a little discouraging to prospective patentees in

1. Camphene is another word almost as ambiguous as 'benzine.' Camphene is the correct scientific name for a definite chemical compound, a solid terpene of the formula ${\displaystyle C_{10}H_{16}}$. Turpentine is a mixture of pinene, also of the formula ${\displaystyle C_{10}H_{16}}$, but a liquid, and other similar substances; purified, it contains a higher per cent, of pinene, but is a mixture still, not pure pinene and certainly not camphene. This appropriation of scientific names by dealers to imply a higher degree of purity than actually exists in their wares is a constant source of confusion and a real hindrance to the dissemination of accurate knowledge.