MECHANICS AND USEFUL ARTS. 87 



great perfection from the instrument ordinarily known as the wet meter, so 

 long as it is duly protected from frost and evaporative heat. Various con- 

 trivances have been suggested and tried for .securing the instrument from 

 these injurious influences. The most general practice is the substitution, in 

 part or in whole, of alcohol for water as the hydraulic seal; but, while this 

 guards against freezing, it gives rise to much inconvenience by reason of its 

 rapid evaporation and want of specific gravity, which oftentimes cause a, 

 sudden obstruction of the flow of gas at the moment when the stoppage is 

 most inconvenient to the consumer. A liquid free from these objections has 

 long been desired, and, after numerous experiments, I had reason to suppose 

 Iliad discovered it in the solution of neutral chloride of calcium. Accord- 

 ingly, in the year 1843, I introduced this liquid into several hundred meters, 

 for the purpose of giving it a fair practical test. It did not freeze at the 

 lowest natural temperature of our climate, and the strong affinity of the 

 salt for water prevented rapid evaporation; while its specific gravity, being 

 greater than that of water, gave full support to the valve-float, and effective- 

 ness to the hydraulic sealing. The results of the first year of trial were 

 entirely satisfactory, and the liquid was then used in all the exposed meters 

 with equally good results. But the expectations raised by two years of trial 

 were dissipated at the end of the third year; by which time the metals of 

 the meter showed such unmistakable evidences of the destructive action of 

 the solution as led to its abandonment. 



More recently I have been giving trial to another liquid, with encouraging 

 prospect of success. It is the inert substance obtained from fatty bodies, 

 and known by the name of glycerine. It is capable of resisting our low- 

 est natural temperature, maintains its fluidity very pertinaciously, and is 

 considerably heavier than water. Should it manifest no injurious action on 

 the meter metals, or other defects, it will completely meet the wants of the 

 instrument. A more direct method of escaping thesje liquid imperfections 

 has been attempted in the so-called dry meter, working on the pi'inciple of 

 the ordinary bellows, with diaphragms connected by flexible joints. A trial 

 of these, on a large scale, during the years 1847 and 1848, revealed imper- 

 fections which impaired their trustworthiness so greatly as to require their 

 entire disuse. Within a few years sundry improvements have been made in 

 the construction of the dry meter, intended to remove the imperfections be- 

 fore mentioned, which seem to have sufficient merit to justify another trial. 

 This has been in progress for nearly three years, with results, thus far, quite 

 favorable; and if these shall be confirmed by longer and more extensive 

 trial, the annoyances that have so long attended this part of gas machinery 

 may be happily terminated. 



COAL-OIL. 



Although the manufacture of gas is rapidly extending in every direction, 

 and the fact is becoming more widely known that in any town containing 

 more than one thousand inhabitants a gas company can with profit be sus- 

 tained, still, at present the number of gas works in operation in this country 

 does not exceed four hundred, and consequently a large demand exists 

 for other means of illumination. Coal-oil from its inexpensivencss, safety, 

 and high photometric value, occupies an important place among the illu- 

 minating agents at present in use, and has given rise to an extensive trade, 

 which cannot fail to be much increased, though at present it is somewhat 

 depressed. 



