DR. DALTON ON THE CONSTITUTION OF THE ATMOSPHERE. 
351 
the diminution for oxygen, when mixed over water ; but this can be considered only 
as a first approximation. One hundred parts of oxygen may combine with 130 or 
360 parts, or any intermediate quantity of nitrous gas, according to circumstances. 
When only 1 or 2 percent, of oxygen are expected I put in 5 or 10 per cent, of nitrous 
gas, and take one third of the diminution for oxygen. When the oxygen (freed from 
carbonic acid) is judged to be 90 or more per cent, pure, I put 100 parts of nitrous 
gas of known purity (say 98 + ) to 100 of the oxygen, and mark the diminution; I 
next put in 40 nitrous and mark the diminution, and so on, till there is manifestly a 
slight portion of nitrous left ; then this is to be removed by a small portion of 
oxygen ; finally, knowing the quantity of azote which was in the nitrous gas, the 
rest must have been introduced by the oxygen. 
In this way I find a perfect agreement, whether the nitrous test or the hydrogen is 
used ; but with common air the residue is so enlarged with azote as to render the 
measuring of it not so accurate. 
Third Method, hy Qitadr [sulphur et of Lime. 
Quadrisulphuret of lime is an excellent test for oxygen, and may be applied to 
common air or to other mixtures of which oxygen is a part, up to the purest oxygen. 
As this and other similar compounds seem to me destined to act an important part in 
chemical operations, it may not be improper here to give some account of their origin 
and their constitution, as far as actual experiments have demonstrated. 
The alkalies and the alkaline earths that are soluble in water have been long known 
to combine with sulphur, both in the dry and humid way. In the last century they 
went by the name of hepar sulphuris, or liver of sulphur, from their colour. 
Scheele was the first to use the quadrisulphuret of lime to abstract oxygen from 
atmospheric air. Lavoisier also made use of the same article ; but it was to De 
Marti of Spain we owe the most successful attempt with the quadrisulphuret of lime 
to abstract the oxygen from atmospheric air. His memoir, printed in 1795, and re- 
printed in the Journal de Physique, vol. lii., 1801, may still be read with interest. All 
the hepars, when dissolved in water, have usually gone by the harsh name of hydro- 
curetted sulphurets in our English works of chemistry since the commencement of the 
present century. 
In 1798 Berthollet published an essay on the nature and combinations of sul- 
phuretted hydrogen, with reference to the part it acts in the sulphurets. Proust 
afterwards controverted some of Berthollets opinions in the 59th volume of the 
Journal de Physique, 1804. Gay-Lussac, in the 78th volume of the Annales de 
Chimie, 1811, gives some important results on the mutual action of metallic oxides 
and alkaline hydrosulphurets ; he finds amongst other results that no sulphates are 
formed, that water is formed, that sulphites or sulphuretted sulphites, and often me- 
tallic sulphurets are formed ; and that consequently it is not possible to obtain the 
simple metallic bases of hydrosulphurets by means of hydrosulphurets of their oxides; 
