LEA

( 122 ) LEA

boiling the nitrat of lead with yellow oxyd andallowing the clear liquor to cool in a well corkedphial (to keep out the carbonic acid of the at-mosphere) by which a number of pearly crys-talline scales separated, which form the subnitratin question. This salt is sweet and astringent,and when a current of carbonic acid is passedthrough, much carbonat of lead separates, andthe nitrat returns to the state of common nitrat.The elements of this subnitrat are stated at19.86 per cent, of acid and 80.14 of yellowoxyd, which very closely agrees with Berzelius .

In the three nitrats of lead just described, 100parts of nitric acid saturate 205.00, 412,9 and930.92 parts of oxyd respectively. The two firstare as nearly as can be expected in the simpleratio of 1 :2, but the third does not coincidewith any simple ratio. In all these the acid isthe nitric and the oxyd is to all appearance theyellow oxyd.

Nitrite of Lead. This salt was first ob-served by Proust, and is obtained by boiling thecommon nitrat of lead with Metallic Lead, asdescribed in our original article, and is con-sidered by Proust as a nitrat of lead the base ofwhich is at a lower state of oxygenation thanthe yellow oxyd, and by Dr. i homson as acompound of the yellow oxyd with an acid at alower state of oxygenation, and is thereforea nitrite of lead. It is obvious that either theacid or the oxyd must be in this state of di-minished oxygenation, since in its preparationthe metallic lead must absorb that portion ofoxygen necessary for its solution from one orother or both of the constituents of the commonnitrat of lead with which it is digested.

This subject has been examined with greatcare by Berzelius and Chevreul , with a remark-able agreement in their results.

When 20 parts of nitrat of lead are boiledin water with 12.4 parts of metallic lead (whichis equal to the lead contained in the salt) thewhole dissolves in some hours into a deep yel-low liquid, which on cooling becomes the yel-low crystallized mass described by Proust. Thisis the Nitrite of Lead. It has indeed a slightexcess of base, so as to act like an alkali onvegetable colours, and therefore might withmore strictness be called a subnitrite, but weshall retain the term of simple nitrile of leadto distinguish it from a subnitrite with a doubleproportion of base, to be presently described.

This nitrite of lead is alto formed whateverbe the proportion of lead employed with thenitrat of lead-, but when the lead is in excess andthe boiling too long continued, a brick-rud salt

gradually appears, which is the proper subnitrtleof lead.

The nitrite of lead forms yellow foliatedcrystals. Its taste is slightly astringent ahdsugary, 100 parts of boiling water dissolve about9f of the salt, but the same portion of cold watertakes up scarcely more than 1 Sulphuric,nitrous and acetic acids decompose this salt andexpel from it nitrous vapour, particularly whenheated. Carbonic acid passed through a solu-tion of this nitrite, partially decomposes it andseparates a carbonated oxyd. Oarbonated pot-ash entirely decomposes it into carbonat of leadand nitrite of potash. When the nitrite is gra-dually heated it loses its acid and passes to thestate of yellow oxyd.

The subnitrite of lead is produced, as abovedescribed, by boiling nitrat of lead for manyhours with more metallic lead than it can takeup: 10 parts of the nitrat by long boiling willthus dissolve about 12 parts of metallic lead,and the solution on cooling lets fall small brick-red crystalline plates, whilst the supernatantliquor contains a mixture of both these nitrites.These brick-red crystals are the subnitrile oflead, and consist of nitrous acid and a doubleportion of yellow oxyd of lead to that of thenitrite. This subnitrite is very little soluble inwater, 3 parts requiring 100 of boiling waterfor solution. It is copiously precipitated bycarbonic acid gas,, or even by exposure to air.M. Chevreul gives the elements of the Nilrile

Nitrous acid

18.15 —

100 .

Yellow oxyd

81.85 —

450.

100.00

550.

the Subnilrite of Lead

Nitrous acid

9.9 —

100.

Yellow oxyd

90.1 —

910.

100.0

1010.

Berzelius agrees pretty nearly with this esti-mation, so that the base of this subnitrite isa double proportion of that of the nitrite.

We shall conclude this article by noticing asingular production of the Peroxyd or Brownox/yd of lead observed by M. Chevreul. Thisoxyd is generally produced, as before mentioned,by digesting minium in nitric acid, by which aportion of it loses oxygen to pass to the state ofyellow oxyd and dissolves in the acid, and theother part gains oxygen and becomes the in-soluble brown oxyd. M. Chevreul has observed