isi 5.) Scientific Intelligence. 305 
_. I mentioned in a preceding volume of the Annals of Philosophy 
that Mr. Trimmer had given mea salt which commonly sublimes 
during the burning of the London bricks, This salt I found to be 
sal-ammoniac. .The same Gentleman lately put into my hands an- 
other substance, which sublimes likewise during the same process, 
though in much smaller quantity. This substance is usually crys- 
tallized in long slender needles. [t has the metallie lustre, and a 
bluish-white colour; but is so delicate in its texture that it can 
scarcely be collected without falling to powder. In its common state 
this substance has a blue colour somewhat resembling that of watch= 
springs, and it has but little of the metallic lustre. 
It possesses the following properties. When heated in nitric acid, 
it effervesces, and is converted into a white powder. Before the 
blow-pipe it readily melts; and if in a state of purity, is speedily 
reduced into a white metallic globule. ‘This globule is soft and 
malleable ; it dissolves with effervescence in dilute nitric acid. The 
solution is colourless; it crystallizes, and throws down a white 
powder when mixed with sulphuric acid or with prussiate of potash. 
Lhe globule is therefore lead. When the substance in question is 
not pure, but mixed with earthy matter, it readily melts before the 
blow-pipe into a dark-coloured glaze; but no metallic globule of 
lead separates from it, though the heat be kept up a considerable 
time upon charcoal. These facts are sufficient to demonstrate that 
this substance sublimed during the burning of London bricks is 
galena, or sulphuret of lead. Indeed, it has exactly the appearance 
of the galena after it has been roasted. 
This galena must be derived from the cinders of the coals used’ 
for burning the bricks. It is very common to observe small strings 
of galena running through coal beds; and unless I am misinformed, 
such strings have been frequently observed in the beds of Newcastle 
coal. As galena is not volatile, at least at the temperature at which 
bricks are burnt, we must ascribe its sublimation in the present case 
to the sal-ammoniac, which no doubt carries it along with it. This 
salt is well known to have the property of carrying along with it 
those metallic bodies with which it happens to come ia contact. 
III. Queries respecting Valves, with a Description of the Valves in 
the Human Body. t 
(To Dr. Thomson.) 
SIR, 
Tn this age of improvement and discovery, every mite that is con- 
tributed to a public journal, if it is only to open the eyes, and afford 
7 degree of stimulus for others to improve from, must be gene- 
ly considered worth acceptance ; and it is principally with this 
latter hope that I submit the following remarks to your readers. 
What 1 am about to communicate has considerably engaged my... 
attention for some time past, and has been the meahs of my con-— 
sulting every author on hydrostatics possibly within my command, 
but wholly without affording me the leust satisfaction as to What J 
Vor, VI, N° IV, U . 
