Chapter XVI: Sulphur

Sulphur, in its aggregate in the earth is by no means an abundant element. Thus its quantity is far inferior to that of oxygen, as is strikingly illustrated by the diagram already presented. (See page 16.) Yet sulphur was recognized by human beings thousands of years before oxygen, which it has already been stated was discovered in 1774. The comparative lateness of the discovery of this latter element, now known to be that one which predominates largely over all others in the earth, is due partly to the fact that free oxygen almost invariably exists in gaseous form and that the idea or notion of gas is one of recent growth. The fact that sulphur was recognized so much earlier is due to many circumstances. _First_: It is found in the earth in the solid condition—a form at once tangible and easy of recognition. _Second_: Its yellow color helps to render it noticeable. _Third_: It exists in the earth in countries which have long been the abode of civilized beings. Thus it was early recognized in Italy. _Fourth_: It occurs in deposits of such a character that it can be readily obtained in a comparatively pure form from them. _Fifth_: It possesses certain remarkable properties some of which would be easily detected even by savage peoples, while others have for centuries excited great interest in the minds of students of alchemy and chemistry. One of these properties is the ease with which it assumes a liquid form—that is, melts—when slightly heated. Another is the readiness with which it takes fire and burns in the air. A third, closely connected with the foregoing, is the striking blue flame produced when it burns. Still another, and not less noticeable, is the choking and disagreeable odor attendant upon this combustion.

Finally may be mentioned a circumstance which for a long time contributed to make it peculiarly interesting to the alchemist, if not to ordinary men: this is the fact that when sulphur is in the pure form it may be burned away without leaving any ashes. In this respect it differs from most other combustible materials. And this property created the impression that sulphur is a sort of principle of fire, and that it somehow exists in all combustible bodies. Indeed it is only for about a hundred years that sulphur has been classified as a distinct elementary form of matter. It is not intended to indicate here that the strong interest of the alchemists in sulphur was mainly referable to the circumstances of its combustibility. Its power of combination with the metals was well known to them, and was recognized as a subject of practical importance and one worthy of careful study and thought.

Natural Sources of Sulphur.

The principal supply of sulphur for commerce is obtained from the volcanic districts of the island of Sicily. Here in fact there are more than two hundred distinct establishments for production of the substance, and they are capable of yielding about two hundred million pounds of it per year.

The fact that sulphur is easily and widely recognized in the earth has already been dwelt upon. But it occurs in nature in a great variety of forms. The first and most striking form is that of free and uncombined sulphur. In this condition it occurs either as masses or as fine powder. Sometimes these materials possess the well-known and easily recognized yellow color of sulphur; sometimes however the color is white or otherwise disguised by reason of some peculiarity of the sulphur itself or else because of the admixture of foreign substances. Deposits of sulphur occur in the most considerable quantities in the neighborhood of either active or extinct volcanoes. Thus sulphur earth occurs near Vesuvius and Ætna, also in the vicinity of the volcanoes of Iceland, in Central America and in the Sandwich Islands. In the region of some extinct volcanoes the soil is impregnated with sulphur to the depth of twenty or thirty feet and such soil is therefore a convenient source of the element.

Purification of Natural Sulphur Ores.

In obtaining sulphur from the earth for commercial purposes, two simple processes are resorted to. By the first method masses of the sulphur earth are heaped up into a pile, in connection with a small amount of fuel and over a shallow depression in the earth. Upon setting the mass on fire, considerable quantities of sulphur escape combustion, and so melt and run down to the ground below the heap. When the fire is extinguished, the sulphur that collected beneath may be secured in a form now only slightly impure.

The second method of purification of the earth is still conducted in Sicily in the following crude manner, though this is quite an improvement upon that just described. A slightly inclined plane of masonry is built upon the ground. Around the edges of this plane a low wall is erected. At the lower side of the plane the wall is perforated. Upon the surface of the plane large masses of sulphur earth are carefully piled up so as to form a well-built heap. When it reaches the proper height its outside is covered all over, first, with small fragments of the same kind of earth, and then with its fine dust. Some sulphur at the lower portion of the heap is then set on fire at several points. The heat from the sulphur that burns melts other portions of it, which then trickle down the spaces between the masses of rock. This melted material, finding the bottom of the pile, runs freely to the lowest portion of the platform, then through the perforations and out into wooden boxes placed to receive it. The heap burns for two or three weeks, at the end of which time the operation is finished. When the mass is cool it is torn down, and a similar pile is erected from fresh portions of the sulphur earth. The objectionable features of this process are at least four. First, the consumption of sulphur as fuel is a wasteful one. But in reply it may be said that no cheaper fuel is accessible where this manufacture is carried on. Again, the great volumes of sulphur dioxide given out by the burning _calcaroni_—as the heaps are called—are injurious to the health of the workmen. Further, these same products exercise a very destructive effect upon all vegetation in their vicinity. In fact on this account the Italian government has provided by law that this work shall not be carried on at all between July 1st and December 31st. Finally the method is not as successful with the richer ores, for they break down into powder which it is difficult to utilize in the calcaroni.

A new and greatly improved method, and one which overcomes all the objections above cited has recently been introduced. In this, the ore is placed in perforated metal baskets and then immersed in tanks containing hot solutions of calcic chloride. Under these conditions the sulphur melts out from its ore and falls to the bottom of the tanks, whence it is drawn out by stop-cocks in a comparatively pure form.

Sulphur is generally subjected to a still further purification. This is conducted somewhat as follows. The crude sulphur, being melted in a suitable retort and over a coal fire, changes into vapor and passes into an apartment constructed of stone or brick, and prepared for the purpose. In this apartment, the sulphur at first condenses on the walls as minute yellow crystals or powder called flowers of sulphur. When the first charge of sulphur in the retort has been completely vaporized a new supply is allowed to run in, this time in the liquid form from a small heater placed above the retort. The waste heat from the furnace melts the sulphur in the heater, from which it flows into the retort (by means of the tube shown in the diagram). When a sufficient amount of flowers of sulphur has collected in the chamber, the fire is extinguished. The purer product is then removed. Afterward the whole operation is repeated.

The refining may be conducted so that the temperature of the condensing apartment may rise considerably; in this case the vapor in it changes to the liquid form. This liquid may be drawn off at the base of the chamber into a small receiver, from which it is ladled into moulds, which give it the form of cylinders known in trade as roll brimstone.

Natural Compounds of Sulphur.

Sulphur is also found in the earth in the form of certain chemical compounds. Some of these are very widely distributed. They may be divided into two classes. The first class—whose representatives are by far the more abundant—includes the metallic sulphides, that is, compounds formed by the direct union of sulphur with some metallic substance. As examples of compounds of this class we mention:

Sulphide of iron (commonly called iron pyrites and having the formula FeS₂).

Sulphide of lead (commonly called galena, and having the formula PbS).

Sulphide of zinc (commonly called blende, and having the formula ZnS).

Sulphide of mercury (commonly called cinnabar and having the formula HgS).

Many other examples of similar import might be given, for it is a well-known fact that most of the heavy metals occur in the earth in combination with sulphur.

The other class of compounds also containing sulphur combined with the metals has usually oxygen in addition. Two examples of this class may be given here—calcic sulphate (commonly called _anhydrite_, and having the formula CaSO₄); also baric sulphate (commonly called _heavy spar_, and having the formula BaSO₄).

Sulphur is very widely distributed in animal and vegetable matters. In these it exists, not as an uncombined element, but in union with others. Indeed such compounds have many other elements besides the sulphur, and they are characterized by decided complexity of structure. But sulphur is oftener a component of animal matters than of vegetable. The presence of sulphur in an egg is proved by an experiment of every-day occurrence. That is to say, the silver spoon with which the egg is eaten becomes blackened. This blackening is due to the production of a new compound formed by a true union of sulphur from the egg, with a part of the metal of the spoon. In fact the black material is sulphide of silver, and it may be represented by the formula Ag₂S. A French chemist has estimated that in the body of a human being of ordinary size there exists, in the aggregate, not far from one quarter of a pound of sulphur. To this, he adds the curious estimate that the entire human population of France may be represented as containing not far from nine millions of pounds of sulphur.

Chemical Properties of Sulphur.

The chemical properties of sulphur may be said to be its most important and interesting ones. That it has a wide range of chemical aptitudes is shown by the fact that it combines in simple forms of union with a majority of the elements known. Thus it has strong affinities for most of the metals. On the other hand it combines with various degrees of attractive force with nearly all the non-metals as well.

Evidently then, sulphur forms a very large number of chemical compounds. While the limits of this work are such as to make it impossible to describe many of them, there are three that may with propriety be briefly discussed in this place, and these are:

Sulphuretted hydrogen (H₂S),
Sulphur dioxide (SO₂),
Sulphur trioxide (SO₃).

Sulphuretted Hydrogen.

This substance is a colorless gas. It has an extremely offensive odor; in fact it is a prominent component of that numerous group of gaseous products of decomposition of animal matters that produce the disagreeable smell attendant upon the decay of the latter.

Again, it is found in the waters of certain natural sulphur springs, and it is a remedial agent of considerable value when properly applied externally or when taken into the stomach. When received into the lungs, however, it is decidedly poisonous.

A considerable number of simple experiments may be tried with it.

In these the gas used is generated by adding diluted sulphuric acid to artificial ferrous sulphide. The ferrous sulphide is usually manufactured by heating a mixture of roll brimstone and iron filings in a sand crucible. In producing the gas, the chemical change is represented by the following equation:

=FeS= + =H₂SO₄=

One molecule of One molecule of
Ferrous sulphide, Sulphuric acid,
88 98
parts by weight. parts by weight.
\___________________________________/
|
186

= =H₂S= + =FeSO₄=

One molecule of One molecule of
Sulphuretted hydrogen, Ferrous sulphate,
34 152
parts by weight. parts by weight.
\________________________________________/
|
186

For the purpose of the experiments here mentioned, a flask or bottle may be used to prepare the gas and convey it into another bottle containing water. In the water, the sulphuretted hydrogen gas dissolves in such quantity that the solution so afforded may be conveniently employed for showing the properties of the gas itself.

The following interesting experiments may be performed by use of this solution:

1. Dissolve in water a small quantity of plumbic acetate, also called sugar of lead. Filter this solution if convenient. To the clear liquid, add some sulphuretted hydrogen water. A black precipitate of plumbic sulphide (PbS) should immediately appear.

2. Dissolve in chlorohydric acid a fragment of white-arsenic not bigger than a pin’s head. To the solution, freely add sulphuretted hydrogen water. A beautiful lemon-yellow precipitate, consisting of arsenious sulphide (As₂S₃), should result.

3. Dissolve in chlorohydric acid a minute quantity of tartar-emetic. To the solution, freely add sulphuretted hydrogen water. A beautiful orange red and flaky precipitate of antimonious sulphide (Sb₂S₃) should appear.

4. Dissolve in water a minute fragment of cupric sulphate, commonly called sulphate of copper or blue vitriol. To the solution, add some of the sulphuretted hydrogen water. This should instantly give rise to a black precipitate of cupric sulphide (CuS).

5. Dissolve in water a small quantity of zinc sulphate. To the solution, freely add sulphuretted hydrogen water. There should appear in this case a white precipitate consisting of zinc sulphide (ZnS).

These few experiments show that sulphuretted hydrogen is a convenient substance for bringing sulphur into union with the metals, and, moreover, they sustain the statements already presented, that many metals show strong affinity for sulphur and marked tendencies to combine with it. For these reasons sulphuretted hydrogen is much used in chemical laboratories for distinguishing one metal from another.[8]

[8] See Appleton’s Qualitative Analysis, published by Cowperthwait & Co., Philadelphia; p. 14.

Sulphur Dioxide.

When sulphur burns in oxygen gas or in atmospheric air, it gives rise to a new gas of choking and offensive odor. This is the same substance as that produced in the first stages of the burning of a sulphur match. It is a substance of considerable importance in the arts, first, because it is always produced in one stage of the process used in the manufacture of sulphuric acid. Now sulphuric acid (commonly called oil of vitriol) is a commercial product of enormous consumption. (See page 152.) Again, sulphur dioxide is used, as such, to a considerable extent in the arts, the principal uses being in the bleaching of straw and woolen goods. Chlorine as a bleaching agent has already been discussed, but it is used mainly for the bleaching of cotton and linen goods; it has an unfavorable and injurious action upon straw and woolen goods.

The way in which these latter are bleached by the use of sulphur may be illustrated by a very simple experiment. Place a few fragments of roll brimstone in a small crucible. Heat the crucible carefully until the sulphur takes fire. Then cover the burning sulphur with a glass lamp-chimney, or any other suitable contrivance. In the top of the chimney hang a moistened carnation pink or other red flower. A few minutes exposure to the gas, results in a partial bleaching of the flower.

On a commercial scale, the sulphur bleaching process is conducted in practically the same manner. For bleaching woolen goods there is provided a small wooden house having a brick floor, with a small pit in the centre. The goods are hung up in this house. The pit is filled with sulphur which, when all is ready, is set on fire by throwing a piece of red-hot iron upon it. Now the doors and windows of the house are closed. Of course the sulphur burns into sulphur dioxide. The operation is allowed to proceed without any further attention during one night. The gas distributes itself throughout the goods and bleaches them. The next morning the doors and windows are opened, and, when the fresh air has driven the sulphur dioxide from the chamber, the goods are found bleached. Everyone knows, however, that this bleaching has not the permanence that chlorine bleaching has. Thus white flannels very soon return to their original yellowish shade.

Sulphur dioxide is placed by the chemist in the class of acid _anhydrides_. This term is intended to carry the meaning that substances belonging to this class combine with water to form acids. In accordance with this form of expression, sulphur dioxide is also called _sulphurous anhydride_. Plainly this means that sulphur dioxide with water will form an acid. Such seems to be indeed the case, for water has the power of dissolving large quantities of sulphur dioxide, and when it does so the water acquires the characteristics of an acid. In fact it is then called sulphurous acid. The chemical change is represented by the following equation:

=SO₂= + =H₂O= = =H₂SO₃=

One molecule of One molecule of One molecule of
Sulphur dioxide, Water, Sulphurous acid,
64 18 82
parts by weight. parts by weight. parts by weight.
\___________________________________/ \______________/
| |
82 82

One special characteristic which justifies the name sulphurous acid, is the fact that the solution so produced has the power of producing a series of salts as the other acids do. In this case, the salts have the general name sulphites.