If the method of writing between the lines in chemicals presented itself to Mrs. van Warmelo’s mind for a moment, it was dismissed as too crude and well-known, and, in consequence, too dangerous.

And yet she found her thoughts reverting persistently to chemicals as the only solution to the problem before her. One day she took the strained juice of a lemon and wrote a few words with it on a sheet of white paper. When dry, there was no trace of the written words to be seen until she had passed a hot iron over them. Imagine her joy and satisfaction when they showed up clear and distinct, in a colour of yellowish brown. Well satisfied with her experiment, she sought and found a square white envelope of thick paper and good quality, which she carefully opened out, by inserting and rolling the thin end of a penholder along the part that was glued. Spreading the envelope before her on the table, she wrote some sentences in lemon juice on the inside, folding it into shape again and pasting it down with great care and neatness. This envelope she placed in Hansie’s hands, with an expectant look, when the latter came home that afternoon.

Hansie turned it over, examined it on all sides and shook her head, puzzled.

“Open it,” her mother suggested, “and look inside.”

Hansie opened it and, peering into it, shook her head again, more mystified than ever.

“I give it up, mother,” she said. “Come, don’t be so mysterious tell me what it all means.”

Mrs. van Warmelo then took the envelope, opened it with the penholder again, and, producing the hot iron which she had been keeping in readiness for the psychological moment, she ironed out the flattened sheet and revealed to the astonished gaze of her daughter the written words within.

At first Hansie was speechless with admiration; then she threw her arms round her mother and hugged her vigorously.

“Really, mother,” she exclaimed, “I am proud of you. How we shall be able to dupe ‘Miserable Renegade’ now!”

The full importance of this discovery was not realised at the time, for all their smuggling had hitherto been carried on merely for pleasure and they had had no information of any importance to communicate to their friends across the seas; but, in the light of after-events, they realised that they had been led to make their preparations and to have their methods in full working order before the time came to use them in conveying dispatches from the Boer Secret Service to President Kruger in Holland.

They were now in the possession of a scheme which defied detection, and the next thing to be done was to inform some distant conspirator of this valuable discovery and instruct him in the use of it.

That this could not be done through the post, my reader will understand, and as reliable opportunities were becoming more rare, Hansie had to wait some months and to possess her soul in patience until at last some trusted friend, leaving the country, could be persuaded to convey the important instructions.

When and how they were eventually sent I cannot tell with positive certainty. There is a difference of opinion on this point between Mrs. van Warmelo and her daughter, and there is no way of settling the dispute, because Hansie’s diary contains no word about the White Envelope, for reasons which it will hardly be necessary to explain.

Mrs. van Warmelo says the instructions were dispatched in a false double-bottom of an ordinary safety match-box. Hansie thinks they were either hidden behind a photo-frame or in a tin of insect-powder, both these methods having been employed on various occasions, but at present we are only concerned with the fact that the instructions reached their destination safely, and from that day until the end of the war a gloriously free and uninterrupted communication was kept up between Harmony and Alphen and one spot in the north of Holland, of which we shall hear more as our story unfolds itself.

Further experimenting showed that the lemon-juice became visible after a few days when written on certain papers, while on others there was nothing to be seen after many weeks, and this danger was immediately communicated to Holland as a very serious one, for it stands to reason that the danger connected with the sending of the White Envelope from South Africa was nothing compared to the danger of receiving one and having it censored three weeks after it had been written.

One had to keep in mind that letters leaving the country would be censored immediately and would not be subjected to further scrutiny in Europe, whereas letters for South Africa ran every risk of being betrayed on examination, after a three-weeks’ journey by land and sea.

When the smuggled instructions were well on their way, the first White Envelope was written to Holland, and carelessly thrust amongst a pile of other letters by the quaking Hansie when next she handed her mail to “Miserable Renegade.”

He glanced through them all without examining them, merely putting the mark of the censor on them and assuring Hansie that they would be forwarded that very day.

No seven weeks could have been longer or more full of suspense than those which followed, and the excitement at Harmony when in due time a square white envelope in the well-known hand arrived from Holland can better be imagined than described.

With what anxiety it was opened and how eagerly examined before the hot iron was applied! how keen the delight when nothing legible was found, even on the closest inspection! What relief, at last, when the written messages became not only legible, but clear and distinct!

So this method was going to answer beyond their wildest expectations!

To make assurance doubly sure, and because Hansie did not trust “Miserable Renegade” one jot, she sometimes made use of friends, going to Johannesburg, to post her White Envelope there, giving as her reason for doing so the difficulties she had had with the Pretoria censor.

Of course the secret of the White Envelope was not confided even to her most intimate friends.

This correspondence having been fairly established, there was nothing to prevent Hansie from using the European mail every week; but to avoid needless risks and the possible exposure of the valuable secret, it was agreed to use it only in cases of extreme necessity.

The sign of the White Envelope became an understood thing between the conspirators, and for all other correspondence grey and coloured envelopes were used.

The correspondent in the north of Holland was a young minister of the Gospel who had taken for years an unusual interest in Hansie’s career.

At this point of our story the two young people, after some years of estrangement, brought about by an unfortunate misunderstanding on his part, pride and self-will on hers, had reached the delightfully unsettling stage of exchanging photographs, the sequel of which took place under the most romantic circumstances, not to be related in this volume.

“It is an ill wind that blows nobody any good,” the young man must often have thought, as he faithfully carried out every instruction from the scene of action.

All communications for the President and Dr. Leyds were sent to him (through the White Envelope), because it was not considered safe to correspond with them direct, even through the medium of the lemon-juice discovery.

As time went on, this method of communication was used for many purposes and always with success, but some time after the war, when it was Hansie’s right and privilege to go through the war correspondence of the young minister of religion, she came upon a letter from Dr. Leyds to him, in which she read, with growing interest, the following information:

“I cannot conceal from you that I was startled when I opened the last white envelope, for I was able to read the whole report, though the writing was faint, without applying the heating process to it. Perhaps this letter lay in a warm place near the engine-rooms on the voyage. Will you not send a timely warning? You could, for instance, say that the measles have come out and are plainly visible, even without the application of hot compresses. Those people are quite clever enough to understand what you wish to convey to them.”

This warning did not reach Harmony at the time. Perhaps the censor, trained as he must have been in the art of reading dangerous meanings into seemingly harmless sentences, decided in his own mind that it would be advisable to keep the information about the measles to himself, and consigned the letter to the waste-paper basket.

In time experience taught the conspirators at Harmony that the greatest care would be necessary in the use of the White Envelope, and to this they probably owe the fact that it was never found out by the enemy.

The reproductions given here of specimens of the White Envelope, showing the address on one side and the written messages on the other, will give the reader an idea of how this correspondence was carried on. We do not vouch for the accuracy of the information conveyed in the following translation of the contents of this envelope. The figures were quoted from memory, but the general impression conveyed in this report, of the condition of the commandos at the time, is reliable and correct. On the side flaps of the envelope certain love messages were written. These have been covered over with blank paper and are not for publication.