The boiling juice is first completely saturated with finely powdered calcium carbonate, and the resulting precipitate of calcium citrate allowed to subside. When it is repeatedly washed with water and decomposed by dilute sulphuric acid, an insoluble calcium sulphate separates out, and the coveted citric acid remains in solution. This is then carefully concentrated in leaden boilers until a pellicle begins to form, when it is transferred to other vessels to cool and crystallize. Twenty gallons of lemon-juice should yield about ten pounds of the crystallized citric acid.

Tho citric acid is usually obtained from lemons or limes, it exists also in the juice of the gooseberry, strawberry, raspberry, cranberry, currant, cherry, orange, and many other fruits. Citric acid has been prepared artificially by Grimaux and Adam, who started with glycerin, produced chloro and cyano derivatives, and finally got citric acid itself. Recently Carl Wehmer has discovered that sugar solutions, if exposed to the action of certain mold fungi, become transformed into citric acid, and it is thought that this method of manufacture may replace the extraction from lemon juice.

In several of the world's pharmacopoeias citric acid has for its immediate neighbor another of Scheele's discoveriesgallic acid. Gallic acid exists free in nutgalls, in the leaves of the bearberry, in the root-bark of the pomegranate, and other vegetable substances. It is often found combined as a glucoside. It is prepared from the tannin of nutgalls, either by the action of dilute acids or by the change due to mold growths.

Malic acid is likewise in Scheele's Document of Discoveries. It is a deliquescent crystalline compound, with a pleasant acid taste, and occurs in the juice of most sour fruits. The most interesting characteristic of malic acid is the fact that it furnishes us with a remarkable example of physical isomerism, for when naturally obtained it rotates the plane of polarization, but when artificially prepared is optically inactive.

On oxidizing sugar with nitric acid, Scheele obtained an

organic acid which he named saccharic acid, now called oxalic acid. Oxalic acid is almost universally distributed thruout the vegetable kingdom. From water and carbon dioxide, by means of sunlight and chlorophyll grains, plants build up this compound.

The acid then combines with calcium carbonate and forms the crystalline calcium oxalate so valuable to the pharmacognoscist as a means of recognition of powdered drugs.

Because of the certainty and celerity of its action, oxalic may supplant carbolic acid as the favorite of suicides when the dreaded phenol — on account of its ceaseless havoc among the laity — is altogether ousted from pharmacy. Oxalic acid can kill a human being in three minutes. Because of its resemblance to Epsom salts it has on several occasions been taken in mistake for that much-used saline purgative.

The only acid Scheele discovered which is called by his name is Scheele's dilute hydrocyanic acid (prussic acid), obtained by him from Prussian blue. It is four or five per cent., the official acidum hydrocyanicum dilutum of our pharmacopoeia being half that strength. In the concentrated form it is a rarity to be found only in the laboratories.

Prussic acid is found in the pits of apples, in the kernel of the peach and in the leaves of the laurel. If these are consumed in quantities, alarming- even if unexpected - illness may result. The acid occurs also in bitter almonds, and when their pulp is distilled we obtain the most poisonous of our official oils. Prussic acid is another standby of those intent on self-destruction, not only in real life, but in fiction. For instance, in Grant Allen's The Woman Who Did, the heroine Herminia after being abused by her daughter - kills herself by drinking prussic acid. A remarkable feature of this deadly poison is the astonishing rapidity with which it causes death. A thief, who was pursued, swallowed a dose, staggered a few steps, fell to the ground and expired. A drop of the pure acid can kill a frisky dog in a second. Professor Doremus in an interesting letter to the Standard Dictionary,

says: 'I have held a drop of anhydrous hydrocyanic acid on a glass rod and brought it toward a live rabbit. Before it reached the animal, he dropped dead from inhaling the vapor.'

It is said that Scheele himself was suddenly killed by inhaling the vapors of the terrible poison he discovered, but while we hardly think this is the fact in his case, it is true that it has ended the career of more than one subsequent chemist.

The series of experiments which Scheele conducted in connection with Prussian blue — laying the important foundation of our present knowledge of the cyanides - has excited the enthusiasm of modern chemists, and with a tribute on this topic from the learned pen of Professor John Ferguson of the University of Glasgow, we close our meagre account of Scheele's momentous work:

In 1782-1783 appeared a research which of all those Scheele conducted exhibits his experimental genius at its very best. By a wonderful succession of experiments he showed that the coloring matter of Prussian blue could not be produced without the presence of a substance of the nature of an acid, to which was ultimately given the name of prussic acid. He showed how this body was composed, described its properties and compounds, and mentioned its smell and taste, utterly unaware of its deadly character. Nothing but a study of Scheele's own memoir can give an adequate notion of the manner in which he attacked and solved a problem so difficult and complicated as this was at the period in the history of chemistry when Scheele lived. His accuracy, qualitative and quantitative, considering his primitive apparatus, his want of assistance, his place of residence, the undeveloped state of chemical and physical science — was unrivaled. He grudged no labor to make the truth indisputable; and he evidently never considered his work complete about any body unless he could both unmake and remake it. For him chemistry was both an analytic and a synthetic science, and he shows this prominently in his researches on Prussian blue.

The one aim of Scheele's life and he never swerved from it was the experimental discovery of the truth in nature.'

This was Scheele's aim. Whose aim was higher? This is what Scheele did. Who has done better?

High are the pointed peaks of Sulitelma, O Sweden! where the cooling cataracts rush down the crags of the mountain. In the Baltic is the island of Oland, whose rocks of Silurian limestone have battled for centuries with the god of storms. Near the North Cape rises a mighty slab of granite, thousands of feet in height, with every niche containing the nest of an Arctic bird. Calm are the waters of Mælar, and the falls of Motala turn the wheels of many mills. The lake of Vener is large, and Tornea Elf flows down to the sea. Famed is the hill of Kinnekulle, and who knows not the forest of Kolmorden? Uto is rich in the ores of iron; copper is found in Falu, and silver at Sala. There are mines of magnetite and hyperite, of granulite and dolomite. Among the trees of fir and pine the elk and roe deer search for browsage, and the fleet-footed hare leaps thru the brush. Droves of leaping salmon crowd the rivers, and the herrings swim from the sea to spawn in the shoals. Over the snowy fields the great-horned reindeer wander, the whooper swan sails in the lakes of Lapland, and high in the frosty air soars the gyrfalcon and the golden eagle. Great indeed is the spectacle of the Midnight Sun, and when the Aurora Borealis flashes its dancing columns across the startled skies, the beholder stands with reverent heart and uplifted hand.

Yet boast not of these things, Sweden. Huge kings have sat on thine ancient throne, and hurled stout armies at the frightened nations. But be not proud of them. Do not sing of the Olafs and Erics, and seek not to perpetuate the memories of the vikings of old. We are sick of the bloody sagas of the skalds, and the fierce berserkers who cried Was-hæl among the reddish fords. We have heard quite enough of your battle-axes, and we close our ears at the sound of the

hammer of Thor. Forget that victory at Narva, and scratch out the name of Charles XII.

Sweden, thou hast a greater glory. Thy name is on the lips of thinkers, and when the spirit of Science calls the roll of nations who have served her, thou canst answer in a triumphant voice, for Scheele is thy son.