Part 2 (1/2)

_Magnesia_--Suppose linesia are present Youa drop of hydrochloric acid if the liquid becomes muddy Then add ammonia and ammonium oxalate, when lih blotting paper, and to the clear filtrate add some phosphate of soda solution A second precipitation proves the presence of nesia

_Sulphates_--A solution of bariuives a white turbidity

_Chlorides_--A solution of silver nitrate and nitric acid gives a white curdy precipitate

_Test for Lead in Drinking Water_--I will, lastly, give you a test that will be useful in your own ho through lead pipes Place a large quantity of the water in a glass on a piece of white paper, and add a solution of sulphuretted hydrogen and let stand for some time A brown colour denotes lead Of course copper would also yield a brown coloration, but I a that the circumstances preclude the presence of copper

I have already said that rain water is the purest of natural waters; it is so soft, and free from dissolvedwater to purify it, wethe steam in, since it is a fact probably not sufficiently well known, that the softer and purer a water is, the more liable it is to attack lead pipes Hence a coil of lead pipe to serve as condensing ould be inadoater from Loch Katrine still more so, are more liable to attack lead pipes than the hard London waters To illustrate this fact, ill distil so the water with our reagent, the sulphuretted hydrogen water, a brown colour is produced, showing the presence of lead On condensing in a block tin worm, however, no tin is dissolved, so tin is safer and better as the material for such a purpose than lead

_Filtration_--We hear a great deal about filtration or filters as universalwater Filtration, we must remember, will, as a rule, only remove solid or suspended impurities in water For example, if we take some ivory black or bone black, and mix it ater and afterwards filter the black liquid through blotting-paper, the bone black reh

Filtering is effective here If we take soo solution, however, and pour it on to the filter, the liquid runs through as blue as it hen poured upon the filter Filtering is ineffective here, and is so generally with liquids containing enerally,” and so the question is suggested--Will filtration of any kind remove matters in solution? This question I will, in conclusion, try to answer Bone charcoal, or bone black, has a wonderful attraction for anic matters such as colours, dyes, and coloured iar solutions, etc For example, if we place on a paper filter soo solution, after first war the latter with soh clear, all the indigo being absorbed in some peculiar way, difficult to explain, by the bone black, and re on the filter This power of charcoal also extends to gases, and to certain noxious dissolved organic impurities, but it is never safe to rely too th becoradually cease to act These filters need cleaning and renewing from time to time

LECTURE V

ACIDS AND ALKALIS

_Properties of Acids and Alkalis_--The naiven to a class of substances,an acid or sour taste, and capable of turning blue litmus solution red All acids contain one orreplaced by en atoms are completely replaced by metals, there result so-called neutral or nor no action on litmus solution These salts can also be produced by the union of acids with equivalent quantities of certain metallic oxides or hydroxides, called bases, of which those soluble in water are termed alkalis Alkalis have a caustic taste, and turn red litmus solution blue

In order to explain what is called the law of equivalence, I will remind you of the experiht iron, being placed in a solution of copper sulphate, becaht of ironto the saht of soda would always require a certain specific equivalent weight of an acid, say hydrochloric acid, to neutralise its alkaline or basic properties, producing a salt

The specific gravities of acids and alkalis in solution aretheir strengths and commercial values Tables have been carefully constructed, such that for every degree of specific gravity a corresponding percentage strength of acidity and alkalinity iven in Lunge and Hurter's _Alkali-Makers' Pocket-Book_, but for ordinary purposes of calculation in the works or factory, a convenient relationshi+p exists in the case of hydrochloric acid between specific gravity and percentage of real acid, such that specific gravity as indicated by Twaddell's hydroe of real acid in any sample of hydrochloric acid

The point at which neutralisation of an acid by alkali or _vice versa_ just takes place is ascertained very accurately by the use of certain sensitive colours At first lit crude alkalis containing alumina and iron, it was found that lakes were formed with these colours, and they becoer sensitive The cheed to resort to certain sensitive coal-tar colours, which did not, as the dyer and printer knew, fore, fluorescein, Congo red, phenolphthalein, and so forth

For deterth of coht of the sample is dissolved in water, and a few drops of a solution of e are added, which colour the solution yellow or orange Into this solution is then run, froraduated tube, a standard solution of an acid, that is, a solution prepared by dissolving a knoeight of an acid, say hydrochloric acid, in a known voluradually until the yellow colour changes to pink, at which point the voluht of acid contained in this voluard to the law of equivalence mentioned above, it is an easy matter to calculate the amount of alkali equivalent to the acid used, and from this the alkali contained in the sample

_Sulphuric Acid_--The first process forso so sulphur It was next discovered that bywith the sulphur soiven quantity of brilass carboys were used, but in 1746 the carboys were replaced by cha water at the bottom, and in these lead chambers the mixture of sulphur and nitre was burnt on iron trays Next, although gradually, the plant was divided into two portions--a furnace for burning the sulphur, and a cha the vapours The system was thus developed into the one followed at the present time The sulphur, or, in most cases, cupreous iron pyrites (a combination of iron and copper with sulphur), is burned in specially constructed kilns or furnaces, and the hot gases, consisting essentially of sulphur dioxide with the excess of air, pass through flues in which are placed cast-iron ”nitre pots” containing a ases thus becoen, and, after cooling, are ready forwith steam or water spray in the lead chaen enable the for the part of oxygen-carriers Sulphuric acid is foren with sulphur dioxide and water; the oxides of nitrogen coen of the air present in the chaen to the sulphur dioxide and water or steaen, and so on The exact processes or reactions are of course much more complicated, but the above represents what is practically the ulti the last lead chamber in which the formation of vitriol is effected, must still contain nitrous fumes, and it becomes a matter of iain To effect this object, use isvitriol The gases froh what is called a Gay-Lussac tower (the process was invented by the eminent French chemist Gay-Lussac), which is a tower made of lead, supported by a wooden fra, over which strong vitriol is caused to flow

The vitriol dissolves the nitrogen oxides, and so-called ”nitrous vitriol” flows out at the base of the tower The recovery of the nitrogen compounds from the nitrous vitriol is effected in Glover towers (the invention of John Glover of Newcastle), which also serve to concentrate to some extent the weak acid produced in the lead chaases from the sulphur burners or pyrites kilns The weak chamber acid is mixed with the nitrous vitriol from the Gay-Lussac tower, and the mixture is pumped to the top of the Glover tohich is of sienerally packed with flints This Glover tower is placed between the sulphur burners or pyrites kilns and the first lead cha down the tower ases from the kilns, and a threefold object is effected: (1) The nitrous fumes are expelled from the nitrous vitriol, and are carried into the chaen-carriers; (2) the weak chamber acid which was mixed with the nitrous vitriol is concentrated by the hot kiln gases; and (3) the hot gases themselves are cooled The acid from the Glover tower is purified by special treatment--for example, the arsenic en, in the form of insoluble arsenic sulphide,--and the purified acid is concentrated by heating in glass or platinum vessels

A considerable amount of sulphuric acid is now made by the so-called ”contact process,” in which sulphur dioxide and oxygen unite to form sulphuric acid in presence of a heated ”contact” substance, usually some form of finely-divided platinum

_Nitric Acid_--This acid is usually prepared by distilling a mixture of sodium nitrate and vitriol in cast-iron retorts or pots, the nitric acid being collected in stoneware vessels connected one with another, or, as isapparatus consisting of stoneware pipes or coils cooled by water The effluent gases are passed through a scrubber in order to free the thereater part of the hydrochloric acid manufactured in Great Britain is obtained as an intermediate product in the Leblanc alkali process, which will presently be described, being produced by heating coe quantity is, however, also produced by the so-called direct process of Hargreaves & Robinson, which is, in principle, the same method as that employed in the Leblanc process, except that the intermediate product, vitriol, is not separated It consists essentially in passing the hot gases froh large cast-iron vessels containing coh temperature

Various physical conditions must be complied with in order to make the process a success For example, the salt is used in the form of moulded hard porous cakes made from a damp mixture of common salt and rock salt

The cast-iron vessels ases h the salt in order to ensure uniform distribution The hydrochloric acid is condensed in stoneware pipes connected with towers packed with coke or stoneware

_Alkali: Leblanc Process_--The manufacture of vitriol, as I have described it to you, is the first step in the Leblanc process The next stage consists in the manufacture of sodium sulphate (salt-cake) and hydrochloric acid from the sulphuric acid and common salt; this is called the salt-cake process The production of salt-cake or crude sodiue covered iron pan, called the deco pan or salt-cake pot, is side it is the hearth or bed on which the second stage of the process, the drying or roasting, is effected

The ed into the salt-cake pot, which is heated by a fire below When from two-thirds to three-quarters of the hydrochloric acid has been expelled froe, the h, and at this stage it is raked out of the pan on to the roasting hearth alongside, where the deco directly on to the top of the charge The hydrochloric acid evolved during the process is condensed in reaves & Robinson previously described It is a curious fact that in the earlier years of the Leblanc process, hydrochloric acid, or ”spirits of salt,” as it is frequently called, was a by-product that required all the vigilance of the alkali-works inspectors to prevent it being allowed to escape froulated amount Now, it is the principal product; indeed, the Leblanc alkali maker may be said to subsist on that hydrochloric acid, as his chief instru powder

Mechanical furnaces are now used to a large extent for the salt-cake process They consist broadly of a large revolving furnace-hearth or bed, on to which the ed, and on which it is continuously agitated, and gradually e, by rakes or the like, operated by suitable e of the Leblanc process is the manufacture of ”black ash,”