22. Letters meant to be registered must never be dropped into the letter-box as in the case of ordinary letters, but should be given to the clerk in charge of the post-office counter or window to be dealt with, who will in each case give his receipt for it. The receipt is the sender's evidence that it has been posted in proper course. 23. Letters containing sharp instruments, liquids, &c. or any other articles which would be likely of themselves, or if they should escape, to do injury to the other contents of the mail-bag, should never be posted. Postmasters have instructions not to forward such letters according to their address, but, when observed, to send them to the Dead-Letter Office, from which place they will be returned to the writers. Valuable letters of this forbidden kind, therefore, run great risks of delay, while the articles are liable to be destroyed in their passage through the post.[193] 24. Though the transmission of coin in letters is now absolutely forbidden, except under the registration scheme, arrangements are made for rendering it easy to send small sums by post in postage-stamps. When presented at any of the numerous money-order offices in the United Kingdom, they may be exchanged for money, at a charge of 2½ per cent. Any person wishful to send through the post a sum of money under five or six shillings will find it cheaper to buy stamps and enclose them, in place of a post-office order. One penny will be charged for buying forty stamps, a halfpenny for twenty stamps. 60,000_l._ worth of postage-stamps were bought from the public during the year 1862. 25. In sending postage-stamps in letters, care should be taken to use _thick_ envelopes, so that enclosures of this kind may neither be seen nor felt. It is easy to feel a quantity of postage-stamps in a letter sent in a thin and crisp envelope, and some official becoming aware of this may not be able to resist the temptation to appropriate them. 26. No enclosures whatever should be sent in newspapers impressed with the regular newspaper-stamp. Even an old address of such a newspaper should be carefully cut out. It is not enough that it be obliterated with the pen, as the rules forbid writing of any kind in addition to the mere address.[194] With newspapers stamped by the ordinary postage-label the arrangements are quite different. Any printed paper or manuscript may be folded up with the newspaper on which an ordinary penny-stamp is placed, provided the total amount of the package does not exceed four ounces. The old address (supposing the newspaper has circulated through the post before) may be left on or not at the discretion of the sender, as this does not interfere with the regulation that nothing in the packet shall be of the nature of a letter. On the other hand, any sentence or message written in ink or pencil on any part of the paper makes the packet liable to the unpaid letter-rate of postage.