Review of Prof. Johnson’s Reporton American Coals. 313 
To the list of American coals should be added one sample of 
“natural coke,” from Tuckahoe, Virginia, sent by Messrs. Barr 
& Deaton ; one sample of artificial coke, made from the Midlo- 
thian coal that had been procured for the use of the Navy, and 
another sample made from Neff’s (Cumberland, Md.) coal,—be- 
sides which, as before remarked, the efficacy of mixtures was 
tested by aseries of experiments; one mixture of one-fifth Mid- 
lothian and four-fifths Beaver Meadow, and another of one-fifth 
Cumberland (Md.) and four-fifths Beaver Meadow. 
The remaining six bituminous coals examined were foreign. 
Two of these were sent by Mr. Cunard, agent of the General 
Mining Association of London,—one of which was from Sidney, 
the other from Pictou, Nova Scotia. The other four samples of 
foreign coal consisted of one Scotch, one Newcastle, one Liver- 
pool and one Pictou, and were purchased by the order of the 
Department of Messrs. Laing & Randolph, extensive dealers in 
coal at New York. 
It will thus be seen that the various coals were obtained from 
those who could be depended upon as furnishing truly the article 
represented. ‘There appears to be no reason to doubt that the 
samples furnished were fair specimens of the various kinds of coal 
found in the market. 
The experiments for the evolution of practical results were per- 
formed in the Navy Yard at Washington City. The apparatus 
consisted of a double flue cylindrical boiler, thirty feet long and 
three and a half feet in diameter,—the flues being ten inches in 
diameter. A cistern whose cubic contents were carefully mea- 
sured, was placed above the boiler to maintain a proper supply of 
water, and by which the quantity of water evaporated during each 
experiment was determined. 'The boiler was furnished with two 
safety valves of the simplest form, with the weights acting directly. 
upon them. ‘These served to regulate the pressure of the steam 
generally, but it was measured by a manometer or mercurial 
gauge, carefully graduated, communicating with the steam in the 
boiler, but under such circumstances as to be free from the in- 
fluence of its temperature. The size of the grate and the area of 
the heating surfaces were all completely measured. The draft 
was determined by a syphon draft-gauge and other means. A 
register of the barometric, thermometric, and hygrometric con- 
dition of the atmosphere was constantly kept. A thermometer 
