1819.] Dr. Thomson on Oxymuriate of Lime, 185 
chlorine was united not to calcium, but to lime ; and that, there- 
fore, the bleaching salt of Mr. Tennent is in reality a chloride of 
lime, as it has hitherto been supposed to be. When itis heated, 
the lime parts with its oxygen, and is converted into calcium, 
and the chloride of lime becomes a chloride of calcium. Of 
course it loses its peculiar properties, and, when dissolved in 
water, is nothing else than a muriate of lime. 
Hence the reason that during the preparation of the bleaching 
powder, it is necessary to keep the temperature of the lime very 
low. If it be allowed to acquire heat, the chloride of lime is 
converted into chloride of calcium, and becomes useless for the 
purposes of the bleacher. Probably unslacked lime might be 
united with chlorine, if its temperature could be kept low. But 
when the attempt is made on a large scale, so much heat is 
always generated that the lime is speedily converted into calcium, 
and the object frustrated. 
2. I find that barytes, strontian, potash, and soda, may be 
united to chlorine as well as lime, so that chlorides of these 
bases exist. They are easily obtained by double decomposition 
‘from chloride of lime. When heated, they give out oxygen gas, 
and are converted into chlorides of barium, strontium, potas- 
sium, and sodium. It is probable that many of the metallic 
oxides are capable of forming chlorides likewise. Indeed from 
the trials which I made, I have little doubt that solution of 
chloride of lime may be employed with advantage to procure 
several of the metallic chlorides in quantities and with facility. 
But the discussion of these and many other points, I must leave 
till a future opportunity. 
Articre III. 
On the Reduction of Lunar Distances for finding the Longitude. 
By Dr. Tiarks. 
' (To Dr. Thomson.) 
SIR, Chateangay Woods, North America, Sept. 19, 1818. 
Tue method of determining the iongitude by observations-of 
lunar distances is by far not so commonly practised as it might 
be expected, considering the number of instruments fit for such 
purposes which are in common use. The calculations which 
such observations require are a great obstacle with most people. 
Mendoza’s tables, by which they are very much abridged, do not 
seem to be in general use; and the methods contained in the 
common books, besides being often very inaccurate, require not 
unfrequently more labour and rules than the direct formule. 
Seamen commonly compute by different methods, in order to 
guard against mistakes ; but in cases of a disagreement of the 
