SCIENCE. 



'7 



J_ 



I/{D a -D c ) 



(2) 



and the velocity in the flue will be found from the ex- 

 pression 



(3) 



or, 



V 



(4 



Z> = 



(6) 



But from the Mariotte-Guy Lussac law we have — 



A _ T\ 



substituting this value of D c in formula (4) then results- 



T 



V 



■i 1 



(7) 



In this expression the theoretical velocity of flow is 

 expressed in terms of the height of the flue and the abso- 

 lute temperatures of the flue air and the external air. 

 From formula (7) we have — 



T — T 



27// 



(8) 



The quantity of heat transferred to the air may be rep- 

 resented by 



* = W.c.(T e - T a ) . (9) 



in which <f> represents the quantity of heat in units of heat 

 per second, and c the specific heat of air at constant 

 pressure (c — 0.238.) 



All of the above formulas are well known. The fol- 

 lowing are believed to be new : 



The quantity of heat imparted to the air may also be 



si in which is the quantity 



represented by 'P' — ' r ' 



3600 



w. c. (r c - r a ) 



of heat imparted per second, and as from the nature of the 

 problem *p = <p' we have 



^. r. (7\ - T a ) = 

 3600 



= S.r. (T- 

 W. c. 3600 



combining this equation with (8) we have- 

 jT t — VJ = V't . 

 3600 2g H. 



V*. W.c. T„ 



7]. 



S. 



(10) 

 (ii) 



x T„ 



and 



S = 



2gH.r.{ T,- T a ) 

 3600 



(12) 

 (13) 



This expression gives the total heating surface in 

 the pipes in terms of the velocity, the height of the 

 flue, the weight of air discharged per second, and the 

 absolute temperature of the external air. 



If we substitute for V its value in terms of V, the 

 actual velocity, we have — 



s , _ V* W. c. T a 

 ~ 2gH. r.{T t - T a ) 

 3600 



(14) 



and since 



W. = 



S = 



D c V. A. 

 K '- V s 



A. T n 



igH. r.{T s - T a ) 



(15) 



3600 



another expression for S'. 



These two expressions exhibit the laws of the move- 

 ment of the air, giving the quantity of heating surface re- 

 quired under any special conditions of area and height of 

 flue, temperature of external air, and velocity of dis- 

 charge. 



The constant (/-) may be found approximately from the 

 experiments of Mr. C. B. Richards, made at Colts Arms 



Co., of Hartford. The constant K depends upon the 

 frictiona) resistance which the air encounters in its 

 passage into and through the flues. The velocity Fmay 

 be assumed, and should not be greater than four or five 

 feet per second. The smaller the velocity and the larger 

 the flues, the less will be the required heating surface, and 

 the greater the economy of the apparatus for ventilation. 



The following paper was read by Prof. H. L. Fair- 

 CHILD : 



ON A PECULIAR COAL-LIKE TRANSFORMATION OF 

 PEAT, RECENTLY DISCOVERED AT SCRANTON, PENN. 



The material which we shall notice this evening has 

 naturally been regarded, on account of its associations, 

 as illustrating in some degree the formation of coal. A 

 brief description of that alteration of peat which has 

 resulted in the formation of coal, is therefore desirable. 



Peat results from decomposition of vegetable matter 

 under wate r. The latter excludes the atmosphere and 

 largely prevents the oxidation, which removes the vege- 

 table debris on the upland, and which if rapid we call 

 combustion, or if slow, decay. In northern regions peat- 

 swamp vegetation is commonly a sort of moss (Sphagnum) 

 which grows upward as it dies below. Great peat de- 

 posits are also produced in lower latitudes from the 

 debris of forest trees. The great Dismal Swamp is a 

 fine example, and in the Hackensack and Newark 

 meadows we have examples of peat-formations of great 

 depth, produced by the slow subsidence of the region 

 and the accumulation of salt-marsh vegetation. 



In former geological ages, immense peat deposits were 

 produced in the vast lowlands along the borders of the 

 continents, or at the deltas of the ancient rivers. These 

 great swamps were frequently submerged in the sea and 

 deeply buried beneath mud and sand. This event occur- 

 red perhaps many times in a single locality. The buried 

 peat slowly decomposed. Much of the hydrogen and 

 oxygen of the vegetable tissue, and some of the carbon, 

 were eliminated. The remainder was consolidated by 

 the weight of the superincumbent strata, and the result 

 is bituminous coal. Thus we have the six to twenty coal 

 beds of Pennsylvania, or the one hundred coal-seams of 

 Nova Scotia. 



The evidence that our coals are primarily formed in 

 this manner is abundant, clear and incontrovertible. 

 Few subjects are by our inductive science more definitely 

 settled than this. We find these buried vegetable depos- 

 its in every stage of decomposition and alteration. 

 Where the containing rocks are undisturbed, lying in 

 their original positions, the coal contains a large propor- 

 tion of volatile matter, and is bituminous. But where 

 the rocks are dislocated and folded the coal is, by the 

 pressure and heat, changed to anthracite or perhaps to 

 graphite. The proportion of fixed carbon, or the degree 

 of alteration, is always proportionate to the amount of 

 disturbance which the associated rocks have suffered. 

 Hence anthracite coal is a metamorphosed coal, just as 

 marble is metamorphosed limestone, or quartzyte is meta- 

 morphosed sandstone. The metamorphism of coal is 

 still going on. The escape of the volatile matter, in 

 which the change consists, is observed in the mines, in 

 the production of the explosive " fire-damp," and the 

 poisonous " choke-damp." 



Running from cellulose through wood, peat, and coals 

 up to graphite we have a complete series ; the difference 

 being the loss of hydrogen, oxygen and in a less degree 

 of carbon. This table, after LeConte, exhibits the pro- 

 portions of the elements by weight, the carbon being re- 

 duced to a fixed quantity : 



Carbon. Hydrogen. Oxygen. 



Cellulose 100 16.66 133-33 



Wood 100 12.18 83.07 



Peat 100 9.83 55.67 



Lignite 100 8.37 4242 



Bituminous Coal 100 6.12 21.23 



Anthracite Coal 100 2.84 1.74 



Graphite 100 0.00 0.00 



