JUNCTURE FOR METALLIC PIPES. 285 



tube macle, of the same materials as the larger ones, with 

 a screw at eiu-ji end, wliich is to be made to screvv either 

 into or over them. These screws must be cut in different 

 directions, so that by turning the small tube in one direc- 

 tion, tliey will at the same time screw into both the long 

 "pipes. Should one upon trial be found to screw up to the 

 shoulder sooner than the other, it will be requisite to file a 

 Snrall piece off the end of the longer top, and by this means 

 they may be made to fit accurately, and to screw up ex- 

 actly at the same Instant. If the screvv be cut xipon the 

 lathe, it will only he necessary to move the tool from left 

 ■to right, instead of from right to lelt, as in cutting a com- 

 Uion tcrew. 



At present T have only tried this in a very rough manner, 

 but from what I have" seen, I have not tiie least doubt but 

 it will perfectly answer the end proposed. 



Perhiit me now to ask an explanation of two passages in Q"ery on oxt- 

 yoor ext^}llent Journal, from which I have derived ujuch carbon, and'the 

 pleasure and information, and for which I am hap{>y to era- evolution of 

 , • , . , • f I 1 • Ti • liKlif.gan flora 



bmce tnis opportunity or thankmg you. J he one occurs ui p^yi^sh & irou 



page 50 of vol. XXill, No. 101, May ISOy, and is as fol- filin^^s. 

 lows:' " Oxlgen is found to contain carbon." The f.ther 

 passuge is met with in page 150 of vol. XXII, No. 97, for 

 the same year. They are the words of Mr. Davy — "When 

 *' melted potash is slowly brought into contact with turu- 

 " ings or iron filitig!? heated to wbitf^ness, ludrogen gas is 

 •' evolvedv' . Now as I cannot suppose, that water can exist 

 in any seniible quantity in either melted potash or iron 

 filings heated to whiteness, I am at a loss to account for the 

 presence of hidrogen; especially when I recollect, that pot- 

 ash acted upon by the galvanic battery evolves oxigen. 

 With respect to the first assertion, that "oxigen contains 

 " carbon," T Imve not rnet with it before in any of the trea- 

 "'-es on chemistry which I have read ; bat if either yourself 

 afty-of your num-erous correspondents would have the 

 gootifiess t-o explain these circumstances to a very young cbe- 

 miktf or t-o inform h m vvherehe may meei with a satisfactory 

 t.xc>lai<ation of them, he will esteem it a very great fuvoar, 

 and feel himself much obliged by their ki; dness. 



I have only to add one thing more. In page 312, No. Electrical ex- 



qy pevuneiu. 



