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in the estimation of these particulars. Further, in order properly to represent working conditions, the rate of combustion of the fuel throughout the trial must be the same as that intended to be used in ordinary working, and the duration of the test must be sufficient to include proportionately as much cleaning of fires as would occur under the normal working conditions. The tests should always be made with the kind of coal intended to be generally used, and the records should include a test of the calorific value of a sample of the fuel carefully selected so as fairly to represent the bulk of the coal used during the trial. The periodic records taken are the weights of the fuel used and of the ashes, &c., produced, the temperature and quantity of the feed-water, the steam pressure maintained, and the wetness of the steam produced. This last should be ascertained from samples taken from the steam pipe at a position where the full pressure is maintained. In order to reduce to a common standard observations taken under different conditions of feed temperatures and steam pressures, the results are calculated to an equivalent evaporation at the atmospheric pressure from a feed temperature of 212° F.  (J. T. Mi.) 

Trials of Various Types of Marine Boilers

Description of Boiler.		Grate  Area sq. ft.	Heating Surface sq. ft.	Duration of Trial Hours.	Coal burned Per sq. ft. of Grate per Hour.	Air Pressure in Stoke- hold— Inches of Water.	Chimney Draught— Inches of Water	Water Evaporated per ℔ of Coal.		Water Evapor- ated per sq. ft. of Heating Surface.	Thermal Units per ℔ of coal.	Efficiency  of Boiler %.
								Actual.	From and at 212° F.
								℔.	℔.	℔.
Ordinary cylindrical single-  ended; 3 furnaces; 155 ℔  working pressure; closed  stokehold system.*	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	81	2308	25	14.2	Nil	0.36	8.56	10.26	4.26	14,267	69.7
		”	”	24	13.9	”	0.50	8.84	10.33	4.32	14,697	68.0
		”	”	9	30.3	0.81	0.39	7.93	9.27	8.46	14,686	61.4
		”	”	81/2	29.1	0.65	0.32	8.84	10.34	9.05	14,612	68.4
Ordinary cylindrical single-  ended; 3 furnaces; 210 ℔  working pressure; closed  ashpit, Howden system.**	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	63.2	2876 in boiler, 766 in air heaters	13	20.6	In Ash- pit 1.53	0.58	11.30	12.33	5.14	14,475	82.3
Niclausse water-tube; 160  ℔ working pressure.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	46	1322	8	12.8	Nil	0.20	8.41	10.15	3.75	14,680	66.9
		”	”	8	21.9	”	0.20	8.01	9.40	6.11	14,760	62.1
		”	”	37	20.2	”	0.29	7.62	9.00	5.44	14,600	60.5
Niclausse water-tube;  250 ℔ working pressure.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	34	990	9	14.0	0.10	0.23	8.77	10.50	4.17	14,640	69.8
		”	”	9	22.0	0.27	0.23	7.68	9.06	5.74	14,640	60.4
		”	”	90	15.4	Nil	Not asce- rtained	7.61	9.08	4.00	14,630	59.9
Babcock water-tube; 33/16  in. tubes; 260 ℔ working  pressure.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	36	1010	9	13.0	”	0.26	9.31	11.02	4.30	14,590	73.2
		”	”	9	20.0	0.18	0.20	8.58	10.11	6.13	14,590	67.0
		”	”	90	14.5	Nil	Not asce- rtained	8.09	9.53	4.18	· ·	63.1
Babcock water-tube; 113/16  in. tubes; 270 ℔ working  pressure.***	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	62	2167	28	18.4	”	0.45	8.94	10.61	4.61	14,520	70.7
		”	”	24	19.2	”	0.47	8.93	10.59	4.82	14,390	71.1
		”	”	12	20.5	”	0.42	9.42	11.04	5.41	14,080	75.8
		”	”	7	28.9	0.50	Not asce- rtained	8.54	9.88	6.91	14,390	66.3
		”	”	30	19.9	Nil	0.38	10.11	12.00	6.01	14,530	79.9
		”	”	29	27.1	0.66	0.23	9.96	11.67	8.05	14,630	77.1
Belleville water-tube with  economizers; 320 ℔  working pressure.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	44	910 in boiler;	241/2	15.8	Nil	0.36	9.65	11.46	4.94	14,697	77.2
		”	447 in econo-	24	17.4	”	0.39	9.33	11.00	5.30	14,805	71.8
		”	mizer;	11	19.8	”	0.43	9.39	11.03	6.38	14,578	73.3
		”	1357 total.	8	27.2	”	0.39	8.28	9.79	7.78	14,611	65.0
Yarrow water tube; 13/4 in.  tubes; 250 ℔ working  pressure.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	56	2896	26	16.9	Nil	0.31	9.57	11.45	3.12	14,750	75.0
		”	”	26	18.2	”	0.31	9.37	11.33	3.30	14,500	75.7
		”	”	25	21.3	”	0.31	8.83	10.45	3.63	13,500	75.2
		”	”	30	35.4	0.53	0.26	8.82	10.59	6.04	14,430	70.9
		”	”	8	41.9	0.86	0.31	8.24	9.94	6.69	14,500	66.3
		”	”	8	33.7	0.31	0.30	8.39	9.93	5.47	14,680	65.4
		”	”	8	39.8	0.82	0.24	8.85	10.43	6.81	14,530	69.5
Dürr water-tube; 250 ℔  working pressure.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	71	2671 in boiler, 140 in super- heater; 2811 total.	26	16.1	Nil	0.39	7.95	9.50	3.24	14,500	63.8
		”		26	17.7	”	0.30	7.06	9.28	3.43	14,620	61.7
		”		25	21.1	”	0.31	7.62	9.08	4.05	14,650	60.3
		”		7	33.8	0.70	0.36	7.72	9.29	6.59	14,570	62.7
		”		8	26.7	0.33	0.35	7.86	9.26	5.30	14,320	63.1
		”		8	34.6	1.11	0.20	8.02	9.53	7.02	14,230	64.8
		”		22	34.8	0.73	0.16	6.84	8.06	6.02	14,430	54.0
		”		24	29.9	0.35	0.12	7.62	9.00	5.75	14,240	61.2
		”		20	19.9	Nil	0.21	7.30	8.33	3.66	14,240	58.6

*  In the first three trials no retarders were used in the tubes. In the last trial retarders were used.

**  In this trial retarders were used in the tubes.

*** The first four trials were made with horizontal baffles above the tubes; the last two trials with the baffling described in the text.

Boiler Making

The practice of the boiler, bridge and girder shops may here be conveniently treated together, because similar materials and methods are employed in each, notwithstanding that many points of divergence in practice generally relegate them to separate departments. The materials used are chiefly iron and steel. The methods mostly adopted are those involved in the working of plates and rolled sections, which vastly predominate over the bars and rods used chiefly in the smithy. But there are numerous differences in methods of construction. Flanging occupies a large place in boilermaking, for end-plates, tube-plates, furnace flues, &c., but is scarcely represented in bridge and girder work. Plates are bent to cylindrical shapes in boilermaking, for shells and furnaces, but not in girder work. Welding is much more common in the first than in the second, furnace flues being always welded and stand pipes frequently. In boiler work holes are generally drilled through the seams of adjacent plates. In bridge work each plate or bar is usually drilled or punched apart from its fellows. Boilers, again, being subject to high temperatures and pressures, must be constructed with provisions to ensure some elasticity and freedom of movement under varying temperatures to prevent fractures or grooving, and must be made of materials that combine high ductility with strength when heated to furnace temperatures. Flanging of certain parts, judicious staying, limitation of the length of the tubes,