should be held on a piece of platinum wire in the lower part of a Bunsen flame when, if it contains barytes, the flame will be coloured green; if strontium sulphate is present a crimson flame will be obtained. This test is not always easy to carry out, but with a little care the coloured flames can be obtained, and they are good proof of the presence of the pigments named. A quantitative analysis of white lead may be made as follows:

Weigh out 2 grammes and dissolve them in a beaker with the smallest possible quantity of pure dilute nitric acid, remove the insoluble matter by filtering, wash the residue well with warm water, adding the first wash waters to the filtrate, then dry the residue, place the filter paper and its contents in a weighed crucible and burn the paper; when completely burnt allow the crucible to cool in a desiccator and then weigh it. From the weight so obtained deduct the weight of the crucible and of the filter-paper ash, the difference is the weight of the insoluble residue.

To the filtrate add dilute sulphuric acid and a little alcohol, filter off the precipitate of lead sulphate which is obtained, wash it dry and burn it in a crucible as before. By multiplying the weight of the lead sulphate so obtained by 0·73554 the weight of lead oxide in the white lead can be found.

The carbonic acid can be ascertained by treating 2 grammes of the white lead with nitric acid in a Schrotter's or other form of apparatus for the estimation of carbonic acid.

The water may be determined by taking the difference between the amounts of lead oxide and carbonic acid thus found and 100. Hygroscopic water can be ascertained by heating 2 grammes in an oven at 110° to 120° C. until no further loss of weight occurs. If the white lead be adulterated with barytes, lead sulphate, china clay or some of the other insoluble white pigments, these will be left behind as an insoluble residue on treatment with nitric acid; their amount is ascertained by filtering off, washing, drying, and burning the residue in a weighed crucible in the usual way. Soluble adulterants like whiting, strontium carbonate, barium carbonate, and magnesite will be dissolved; if the presence of these is suspected, to the filtrate should be added more dilute sulphuric acid, which will precipitate the lead and barium; this precipitate can be filtered off, the two can be separated by boiling with hydrochloric acid, which dissolves the lead sulphate but not the barium sulphate. To the filtrate ammonia and ammonium oxalate are added; this precipitates the calcium and the strontium, while the magnesite (if present) will remain in solution, and can be precipitated by sodium phosphate. It is not necessary to describe in detail the methods of separating these

adulterants any further; some notes bearing on this point will be found in the descriptions of each individual pigment, while reference should be made to works on quantitative chemical analysis, such as that of Prof. Sexton, for fuller details.

By multiplying the weight of the carbonic acid by 5.05 the amount of lead oxide with which it is combined can be calculated; the two amounts added together give the quantity of lead carbonate in the white lead. Deducting the amount of lead oxide combined with the carbonic oxide from the total present, and multiplying this difference by 0.077, gives the amount of water combined with it to form lead hydroxide, and the two amounts added together gives the amount of the latter body present.

Paste White Lead can be quantitatively examined as follows:-Two grammes are treated with strong nitric acid at a gentle heat; this converts all the oil into an insoluble greasy matter, of which no account need be taken; the process then becomes identical with that for dry white lead. Should it be desired to ascertain the amount of the oil, then 10 grammes must be weighed into a filter paper and placed in a Soxhlet or other form of fat-extractor and the oil extracted by means of petroleum ether; the ethereal solution is then run into a weighed glass, the ether evaporated off and the oil weighed. If a fatextractor is not available it will suffice to agitate the white lead with some petroleum ether in a beaker, allowing the pigment to settle, pouring off the liquid into a weighed glass, again pouring on more ether, and again allowing the white lead to settle; the ether is poured off into the glass, or the mass may be filtered. Finally, the ether is evaporated off as before.

It is sometimes recommended to burn off the oil from the white lead in a crucible, but this course is not so satisfactory as treating it with petroleum ether, as not only is the oil burnt off, but the white lead is decomposed; whereas in the ether method the lead is left in its original form for further examination if necessary.

SULPHATE OF LEAD PIGMENTS.

Sulphate of lead, Pb S O4, forms the basis of a number of white pigments which are made on a large scale and sold under a variety of names, such as Patent White Lead, Non-poisonous White Lead, Sublimed White Lead, &c. These do not consist entirely of lead sulphate but contain other bodies, such as zinc oxide, barytes, magnesia, &c., in varying quantities; they are

made by different methods, and most of those now sold are produced by patented processes.

Lead sulphate can be made by dissolving lead in strong sulphuric acid, the action is, however, but slight and does not form a commercial method of manufacture. It is mostly made by adding sulphuric acid to solutions of either lead acetate or lead nitrate; perhaps the best method is that where lead acetate is used.

Metallic lead is granulated by melting and pouring the molten lead into cold water; the object of granulating is to obtain the metal in such a form as to expose a large surface to the action of acids and air. The granulated lead is placed in large tub fitted with a closed steam coil so that the ac

facilitated by heat, if necessary. Acet
own volume of water is poured on to the
acid is at first rather sluggish, but by
on for about 12 hours, then running off
lead in the tub without any liquor, a cer
goes on, resulting in the formation of a
lead, so that when the acid is again adm
acts more rapidly, and a strong solutio
obtained; this action is facilitated by
contents of the tub. From the tub +1
large wooden vessel and to
small quantities at a tim
is thereby precipitated.
phuric acid used is no
that some of the lat
allowed to settle, ar
back again into th
for, as will be seer

acetic acid is re
on between tl
acetic acid can
lead for precipi
acetic acid may b
phate; theoreticall
acetic acid is require
requires to be rest
to time.

The sulphate of lead which is precipitated is washed with water, drained on a filter, and dried; after which it is ready for use as a pigment, or can be combined with other white pigments if desired.

=

The acetic acid used should be as pure as possible; the usual commercial variety of a strength of about 1.050 10° to 12° Twaddell is sufficiently good for the purpose; this contains about 35 per cent. of actual acetic acid, although some makes contain more. 100 lbs. of it will dissolve about 60 lbs. of lead supposing all the acetic acid exerts its solvent power, but in practice this never or but rarely happens, nor indeed is it necessary that it should. From 20 to 28 lbs. of sulphuric acid will be required to

ssolved by this quantity of acetic acid. approximate and are given simply as

hat crystalline, and very heavy powder, g about 6.3. It is only slightly soluble ilute acids and in alcohol, but soluble in 1t and in strong sulphuric acid; from on the addition of water. dissolves it, and crystals cools.

crystalline character ing it often to work ct can be remedied dily acted upon by e permanent than ts solubility being white lead, and, n sold as 66 nongood white, but about equal to

pale chromes. sulphate the base hese are to be found ere they lie buried in ould really be most inventors if they

would peruse these records and see what has been done in the past. A few of these inventions may be briefly noticed here, and a fuller description given of such as are at present used on a large scale.

Richardson, in 1839, patented the use of the sulphate only as a pigment; in 1853, Carter & Marriott prepared a chlorosulphate of lead made by treating 100 lbs. of litharge with 25 lbs. of salt, and the product so obtained with 5 lbs. of sulphuric acid. Woods, in 1866, took out a patent for the preparation of a white pigment from lead fume, which is a mixture of lead, lead oxide, and lead sulphate; this he treated with hydrochloric acid thus forming a chloro-sulphate; or he calcined the fume in a furnace, whereby it was converted into a white mixture of lead oxide and lead sulphate, which was then treated with hydrochloric acid as before. Groves, in 1826, treated galena with potassium nitrate and sulphuric acid, whereby the lead sulphide was converted into lead sulphate, which was dried and sold as a pigment. In 1866, Messrs. Bell & Fell patented the use and preparation of what they called a sub-sulphate of lead, prepared by precipitating a solution of lead nitrate with sulphuric acid and then boiling with an alkali.

SUBLIMED WHITE LEAD.

This product is the invention of G. T. Lewis, and was first patented in 1879. About 1870 a vein of ore containing both lead and zinc, being a mixture of galena and blende, was discovered in America; this was smelted for lead, which, owing to it being different in properties from ordinary lead, was distinguished as "Bartlett lead;" the presence of zinc in lead ores is very detrimental, as the zinc cannot wholly be removed from the lead, while it imparts to it properties which, by causing it to become hard and brittle, prevent its application to those uses for which lead is of great service. The process of white-lead making

now to be described was to some extent devised to utilise this lead-zinc ore.

The manufacture of sublimed lead depends upon two facts, which also are the principles that underlie some of the ordinary processes of lead smelting-first, when lead ore (galena, lead sulphide) is heated in a furnace with access of air it undergoes oxidation, partly to lead oxide, Pb O, partly to lead sulphate, PbSO4, the amount of the oxidation depending upon the amount of air which comes in contact with the ore; if this is small then