44 On the MelaUlc Salts. 



boiler with the longitudinal flue, by introducing vertical tubes 

 into the flue connecting the part above the flue with that below, 

 by means of the said vertical tubes, in the same manner as the 

 upper and lower part of the boiler, represented in Plate I. are 

 connected with each other : or, it tlie boiler be constructed for 

 the purpose, instead of one flue two flues may be carried tlirough 

 it with vertical tubes inserted in each ; (see iig. 3 :) and it will 

 be advantageous that the vertical tubes shoulrl not lange in a 

 .straight line behind each other, i)ut rather take a zig-zag direc- 

 tion as in fig. 2. We are however of oj)iuion, that this boiler, which 

 would be more troublesome to construct than fig. 2 and ^, will 

 not prove more efilicient ; for it is tlie vertical surfaces opposed to 

 the direct anirse of the Jlavie and heated ah., that receive and 

 transmit the principal part of the heat to the water, the vertical 

 sides (which in this ca'ie form the sides of the flue) contributing 

 but little to the efiect, especially where there is room enough to 

 construct a long boiler. There is not, after tlie furnace of a 

 boiler is once fairlv heated, so much waste of heat even by the 

 sides of a brick-work flue as some may imagine ; for the effort 

 of the flame and heated air is to find the most direct course to the 

 chimney ; nor can any method better calculated to prevent this 

 be easily imagined than the one pointed out by Mr. Woolf, 

 namely, to interpose tubes in the way of the draft, that the 

 flame and hot air may be obliged to impinge against them, and 

 give out their heat before they reach the chimney. 



XIV. On the Metallic Salts. By A Correspomjent. 



To Mr. Tillnch, 



Sir, — JL HE proper arrangement of the parts of a science is 

 attended with considerable benefit towards its advancement, and 

 the just definiti(jn of each particular part will not, I presume, be 

 unattended by its corresponding utility. 



To set a doubtful point in our present chemical nomenclature 

 at rest, alone induces nie to trouble you with the following brief 

 remarks: not that I am an advocate for generally received opi- 

 nions, or biassed by any particular theory, but solely actuated by 

 a desire of eliciting truth. 



Your correspondent H. p. 4Gli, vol. xlv. of your valuable 

 Journal, says " that he has continually observed metallic salts 

 to have an excess of acid ;" and concUides " that it is essential to 

 them, and therefore, that there is no neutral metallic salt." 

 Fourcroy corroborates this, when he says, in his admirable work, 

 ()). 69, vol. v. Nicholson's Translation) that " the metallic salts 

 have always an excess of acid/' and II. endeavours with very in- 



gcuious 



