A rubbery question

As one thought leads to another, and I've been reading about rubber lately, I've been wondering this:   why did Goodyear, who invented vulcanisation (and hence the modern era of rubber), even think to put sulphur into rubber?  Why sulphur?  Seems an odd substance to try mixing with indian rubber in the vague hope something good may come of it.

Of course the mega resource of the internet would help.

Turns out the sulphur idea was actually that of another inventor, Nathaniel Hayward, and his account of his involvement in the path towards vulcanisation seems to be set out in a statement at this obscure website:

Sometimes previous to the year 1834 there was a company formed at Boxbury, Mass., to manufacture India Rubber goods. The members of this company were John Haskins, Edwin M. Chaffee, and Luke Baldwin. They had in some way learned the art of dissolving rubber gum, which they tried to keep a profound secret. They soon, however, sold out their interest to a larger company called the Roxbury India Rubber Company, who continued the business in the same place. This company made large preparations to manufacture India rubber goods, and the interest got up with regard to this article in and around the city of Boston was very great. India rubber cloth for carriage tops, overcoats, and other articles to protect such as were obliged to be out in stormy weather, and it was thought would soon come into general use and create a great demand for this fabric.

In the year 1834 Gen. Jackson, then President of the United States, visited New England, and while at Boston was presented with a suit of clothes of this new manufacture, in which dress, on a day somewhat wet, he appeared in public on horseback, for the purpose of reviewing the troops on the Boston Common. This occurrence helped to inflate the bubble, and in a short time the stock of this company rose from one hundred to five or six hundred dollars a share, and every one owning stock in this concern, it was thought, was about to make his fortune.

My curiosity, with that of many others, was highly excited, and I went to the factory and bought rubber cloth for a carriage top. When using the carriage thus covered, I noticed that when two surfaces of this cloth came together, in a warm day, they adhered, in consequence of the softening of the gum. This struck me as quite an objection to the use of the article, and led me to try experiments to obviate it. For this purpose, in the month of August, 1834, among other experiments, I mixed and melted together rubber gum, sulphur, and lampblack; but this mixture, at that time, did not result in anything valuable. I continued, however, as I had leisure, experimenting with this article from August, 1834 till April 1835, showing from time to time small samples of my results to sundry persons engaged in the rubber business, for the purpose of carrying on which many companies were being formed in and around the city of Boston, where I then lived. I was assured, by persons to whom I showed my samples, if I could hit upon any method of preventing rubber cloth from becoming soft and sticky when it was exposed to the sun or otherwise warmed, I might depend on being well rewarded. These assurances from men in whom I had confidence, encouraged me to continue my efforts. I therefore sold out my livery establishment in Boston, that I might be able to devote all my time and attention to the business of experimenting with India rubber.

Still doesn't explain why he thought of adding sulphur at that time!  However, the determination he showed to continue experimenting is pretty admirable:

After closing up my affairs, and paying my debts, I had remaining about five hundred dollars, and a horse and buggy. With this property 1 went out to Easton, my native town, and hired a mill building of Cyrus Lathrop, called the Quaker Leonard Place, at a rent of one hundred and fifty dollars a year. This mill was situated in a retired spot about half a mile from the main road, and not far from Oliver Ames' shovel factory. Here, remote from observation, I shut myself up and entered upon a course of experiments with rubber, and continued it for two months without any satisfactory result.

At the end of this time I was on the point of giving up the whole concern, in utter despair; but finally concluded, before doing this, to make one more trial. For this purpose I put all my chemicals, with which I had been working, into a still of the capacity of fourteen or fifteen gallons, with spirits of turpentine, and drew off about four gallons, into which I put four pounds of rubber gum to be dissolved, and with this solution, I made twelve yards (three-fourths wide) rubber cloth, which looked finely, and which stood the weather perfectly, without melting when exposed to the sun for months. The chemicals I put into the still were white vitriol, blue vitriol, sugar of lead, sulphur and several others, indeed, all I had. This result gave me much encouragement, and I took my rubber cloth and went to Boston, thinking that now I had found out how to make rubber goods that would stand the test. I showed my cloth to a company recently formed called the Eagle India Rubber Company, and they at once offered to give me employment. But I declined entering into their service till I had ascertained, by further trial, that I could make more cloth like the piece I had been exhibiting. I therefore bought a  new supply of chemicals and returned to Easton to repeat the experiment which had proved so successful. To my great disappointment, after numerous trials, variously repeated, and continued for nearly four months, I utterly failed to make anything like the sample I showed to the company in Boston. I then went to work to examine my chemicals separately, with the view of ascertaining their purity. I found impurities in many of them, especially spirits of turpentine and lampblack. The turpentine I found I could purify by thoroughly agitating it with water, and the lampblack by exposure to heat, and thus clearing it of all oily matters with which it is usually connected. The spirits of turpentine thus purified, I found would dissolve the rubber, and purified lampblack being added, and the solution applied to cloth, produced an article which would stand the weather. Upon the strength of this discovery, I engaged to work for this company, on a salary of $1,000 a year.

Finally, we get to him working out that it was the sulphur that was important:

Soon after they began work at Woburn, they expressed the wish that I would make some white aprons, thinking they would sell well. This I attempted to do by using a compound of white lead, magnesia and whiting, with equal parts of virgin or white rubber, dissolved in spirits of turpentine. The aprons looked pretty well, but when warmed would soften and stick, and not being white enough to suit irie, I exposed them to the fumes of sulphur to make them whiter, taking the hint from having seen straw bonnets bleached in this manner. By this treatment the rubber cloth became very white, and made elegant aprons. But in addition to superior whiteness, I noticed that these aprons did not soften and adhere after being exposed to the fumes of sulphur as they had done before such exposure. This gave me the first intimation of the power of sulphur to prevent rubber from becoming soft and adherent when warmed. After this I tried exposing pieces of cloth to the sun that had been fumigated with sulphur, and others of the same kind which had not been thus treated, and found the former' would stand firm while the latter would melt and become sticky.

From this time I tried a great variety of experiments with these articles, in numerous and various combinations, and I found that only when sulphur was one of the ingredients of the mixture, there was no melting or sticking of the rubber cloth. All the time I was working for the Eagle Company, and afterwards while working for myself, I, as I had leisure, was experimenting with sulphur and rubber—and the results, and the way and manner they were brought about I kept entirely to myself. One of these discoveries was that rubber cloth which had been prepared without the use of sulphur, if sprinkled over with sulphur in powder and exposed to the sun, and afterwards washed clean, that this process would fix the gum and prevent it from melting.

After I discovered that it was sulphur, and nothing else, among the articles with which I had been experimenting in combination with rubber, which prevented it from melting and becoming adhesive when warmed, it occurred to me, that this was what made the piece of cloth shown to. the Eagle Company free from the usual objections to this article as then made. But during the four months I was laboring in vain to make a perfect piece of rubber cloth, it never entered my mind that sulphur was of any account in this business, and I did not use it.

The story goes on to explain that Charles Goodyear started sniffing around this factory, and Hayward finally told him that it was sulphur that was the secret to his non sticking rubber products.

And then, apparently, Goodyear accidentally discovered that heating it worked wonders:

He developed a nitric acid treatment and in 1837 contracted for the manufacture by this process of mailbags for the U.S. government, but the rubber fabric proved useless at high temperatures.


For the next few years he worked with Nathaniel M. Hayward (1808–65), a former employee of a rubber factory in Roxbury, Mass., who had discovered that rubber treated with sulfur was not sticky. Goodyear bought Hayward’s process. In 1839 he accidentally dropped some India rubber mixed with sulfur on a hot stove and so discovered vulcanization. 

This discovery, and patenting it, did not lead to an easy ride for Goodyear, though:

Goodyear went on to perfect the modern process of curing rubber-acid mixture with heat, now known as vulcanisation. He received a patent for his process on June 15, 1844. Good years, however, weren’t ahead.

Patent wars, pirates employing his patented process without authorisation, increasing debts (for instance, money borrowed for extravagant displays in London and Paris) and a host of other factors meant that Goodyear never enjoyed the success of the rubber industry. His process would go on to make millions for others, but when he died in 1860, he was still in debt.

Anyway, after all of that:  was sulphur first being added to rubber just a case of Hayward throwing anything into the problem and seeing what (wouldn't!) stick?   Seems so...

Update:  I was just reading a bit about the history of sulphur more generally, and have found the next historical thing I must look up:

The element itself was not isolated until 1809, according to the Royal Society of Chemistry, when French chemists Louis-Josef Gay-Lussac and Louis-Jacques Thénard created a pure sample. (Gay-Lussac was known for his research on gases, which involved him flying in hydrogen-filled balloons more than 22,900 feet (7,000 meters) above sea level, according to the Chemical Heritage Foundation.)

 Gay-Lussac sounds well worth reading about!