The Ironmonger, all along a firm believer in, and supporter; of the claims of the velocipede to public esteem, thus sums up j its merits : Tue velocipede, as embodying the combination I of physical with mechanical power, for the purpose of locomotion, has had its claims to adoption fully vindicated; while [ jas an amusement, it is in many respects superior to horse j riding, cricket, skating, or even rowing. A properly-designed velocipede, allowing, as it does, of the full development of I the chest and lungs, constitutes one of the best aids to the much-desired improvement of the human body. Among I other hygienic advantages, respiration is facilitated, and the muscles of the back and shoulders are relieved from the injurious strain often imposed by habits of stooping. Lastly, j velocipathy—thanks to our alma mater for the term—is the most excellent tonic and appetitizer of the modern Pharma-I coposia. Then as to the danger of running over people, the; velocipede is more under the control of the rider than any; horse-driven vehicle. But it is the country, not the city or i town, that is destined to be the scene of its greatest exploits. Very few have had the opportunity of giving them a trial on our country roads, though there is no longer any doubt of their utility in run In Prance, velocipedes are not only the amusements of the Paris gamins of the Boulevards, but are found to constitute a convenient means of seeing a country j without walking. Pour velocipedes drove up the other day to the Hotel de Prance, at Mans, their drivers having started i together on a tour from Trouville, whence they velocipeded I up to Paris. From the capital they started for Bordeaux, i Perte, Bernard, and Mans, accomplishing, on an average, 30 1 miles per day. This fact testifies fcoilte safety as well as the I speed with which velocipedes may be driven, for it is only reasonable to suppose that somewhat rough ground must have been encountered on the tour. The same periodical states that there are as yet no water i I velocipedes in the English market, but that various addenda,: such as protectors from rain and dust, etc., etc., are in demand. I A French theater announces the pas diabolique, whatever that may signify, to be performed with the prancing and cur- ] vetting veloce at full speed. The passion for velocipede per- : formances is so great, that the Paris Censor has ordered that not more than twelve velocipedes should appear on the stage at any one time. European exchanges show no falling off in the popularity I of the bicycle in Prance, while in England the furore is on the increase. I In this country the popularity of the velocipede gains daily.if.What is wanted in each of our large cities is a velocipede race course. Upon this subject the New York Sun, which daily illuminates its readers upon velocipede matters as well as other subjects of popular interest, says: Outside i of Paris they have a regular velocipede course of a mile circle, with a roadway so smooth and [hard that one Could play billiards on it. The races on this course are crowded with fashionable assemblages, the ladies especially thronging the : grand stand reserved for their use. On this course the extraordinary time of a mile in two minutes and fourteen sec- ] i onds has been accomplished on a 45-in. wheel, French model, j i Now, we have as yet nothing like this course in this country, and one is wanted; and, if properly conducted, it would pay a handsome return on the investment. As regards locality, the Capitoline grounds, Brooklyn, are just suited for the purpose, but as yet no track has been prepared, the expense being rather great. The little experience already had in races —one opponent against another—in this vicinity, proves con- , clusively that such contests would be extremely attractive, j and, what is more, would be well patronised by the reputable I classes of the community. As for velocipede races on horse-1 track courses, the affair at the Union Course showed that any-1 j thing of that kind would lower the standard of the sport, i and, beside, be unprofitable. A horse race is exciting, but; ] how much more so is a contest in fast riding between skillful velocipedists. Eaces of this kind have been adopted as one t of the features of the exercises of the New York Athletic , Club, and with the trials of skill which will take place be-; ] tween rival velocipede clubs, a series of exciting and deeply j interesting bicyle races will be inaugurated for each year, well calculated to attract large and fashionable assemblages j of spectators. Let us have no more races on trotting courses.: Velocipeding now is in respectable hands, and has a reputable. status as a gentlemanly sport and exercise. Let it be kept j so, and do not allow it to be contaminated with the evil as sociations, such as have nearly killed the national game of base ball within the past three years. Owing to the lamentable ignorance of the common laws of phiysiology which prevails among the mass of the com-j munity, empirics find no difficulty in foisting the most absurd notions on the people as medical facts; but we have been surprised to see in the editorial columns of papers sup- posed to be edited by educated men, statements in regard to i alleged injuries riders of bicyles are subject to, which are calculated to make respectable medical men laugh. The i Sunday Mercury had an editorial lately, which actually at-j tribiited Brights disease to the bicycle. The World, too, the the other day, in an editorial snarl at velocipedists, attributed still more fatal results to the poor velocipedes. Now, in the first place, velocipede riding can have no objection urged against it as a cause of any class of injuries to which horseback riding is not equally amenable. But the most absurd charge yet made is that of its causing ruptures and hernia. The majority of the people who talk such stuff have about as much of an idea of what constitutes a rupture as they have of the theory of electrical phenomena. Except caused by a severe fall and consequent strain, a rupture from velocipede riding is an impossibility; and in regard to a fall, a man is as liable to it from that in a carriage, or on horseback, or in a ball field, as in falling from a bicycle. The whole subject of these alleged injuries, however, is the veriest bosh, and it is a disgrace to the editors of the journals who publish sucli paragraphs. Respectable physicians advocate it as a healthy healthy exercise, and practice it too. . Mr. Clow, proprietor oi the Smoky City Rink, at Pittsburgh, has had a bridge made for his rink, which, we think, is the greatest obstruction yet surmounted by a velocipede; it is five feet high at center, t lie inclined sides being but twelve feet long by four wide, giving a rise of one foot in two; this was a dangerous looking affair, having no railing at the sides, and being placed near the middle of the floor, required a steady hand, head, and feet; it was, however, successfully crossed several times at the inauguration of the rink; the younger Pickering letting go the handles just before reaching- the top, guided his machine over, and down and around the room entirely by his feet—two only of the scholars cared to attempt this feat, the first getting sufficient speed on his machine to carry it and him about half way up the incline, from which point he very graciously backed down, the floor receiving him and his veloce considerably mixed. Another member, in whose make-up the word fail seems to have had no part, then tried his try, and passing the upper point came down the incline safely until he reached the floor, when he and his veloce suddenly came to the ground; a second and third attempt proved more successful, and he now wants the bridge higher and longer. A journey on bicycles from Liverpool toLondon, by way of Oxford and Henley, has just been accomplished by two of the Liverpool Velocipede Club On,; the evening of March the 25th, A. S. Pearson and J. M. Cy, the honorary secretary of the club, set off from the shores of the Mersey for a preliminary canter to Chester, from which city they started in earnest on the following morning. After a ride of fifty-nine miles they arrived at Newbridge, near Wolverhampton, where they stayed the night. On Friday the velocipedians, having traversed the Black Country, went on to Woodstock, a distance of sixty-nine miles, where they slept. On Saturday night the tourists arrived in London, feeling none the worse tor their long ride. Their bicycles caused no little astonishment on the way, and the remarks passed by the natives were most amusing. At some of the villages the boys clustered round the machines, and, when they could, caught hold of them, and ran behind until they were tired out. Many inquiries were made as to the name of them queer horses, some calling them whirligigs, menageries, and valaparaisos. Between Wolverhampton and Birmingham attempts were made to upset the riders by throwing stones. The tourists carried their luggage in carpet bags, which can be fastened on by strapping them either in front or on the portmanteau plate behind. The New SSxploslve. The recent disastrous explosion in Paris in a manufactory for the preparation of picrate of potassium, coupled with the fact that there are many other such establishments in which the accident may any day occur, gives a peculiar interest to details simply chemical in their nature. The picrate of potassium is the potassium salt of an acid to which the names trini-trophenol, trinitrocarbolic acid, picric acid, carbazotic acid, picranisic acid, chrysolepic acid, &c, have been given. The acid, a frequent product of the action of nitric acid on organic substances, was discovered by Hausmann in 1788; has been the subject of investigation by Liebig, Dumas, and Laurent; and was first accurately described by the last-named chemist, who proved it to be carbolic acid in which three atoms of hydrogen have been replaced by three atoms of the group No 2. This constitution at once explains the explosive character ot the acid and of its salts. It will be seen that the oxygen, of which there is a large quantity, is nearly all combined with nitrogen. Now, compounds of oxygen and nitrogen are very easily decomposed, especially in the presence of substances having a powerful attraction for oxygen, such as carbon and nitrogen. Gunpowder, for example, is a mixture of a substance containing oxygen united to nitrogen (saltpeter), and a substance having a strong attraction for oxygen (charcoal); while in gun-cotton, nitro-glycerin, picric acid, and the pi crates we have the two united in one compound. Stored up in all these substances is a potential energy which betrays its presence by explosion when the oxygen leaves the nitrogen to unite with the carbon and hydrogen. The picrates differ a 315 good deal as to the rapidity and violence of this decompositon; the picrates of mercury, silver and copper on the one hand burning quickly, like loose gunpowder, and on the other, the picrates of calcium, lead, and especially potassium, exploding with a loud detonation when heated on a flat plate, or when sharply struck by a hard body. The first to make practical application of this property of picrate of potassium was Mr. Whitworth, who used the salt to fill shells to be directed against the armor plating of ships. While picric acid may be prepared by the action of nitric acid on many organic substances, such as indigo, aloes, silk, carbolic acid, or salicin, the most convenient and economical material is the so-called yellow gum, or resin of the Xanthorrhea hastilis, which yields, according to Dr. Stenhouse, about fifty per cent of the crystallized acid. The substance is chiefly used as a yellow dye for silk and wool, and as a means of distinguishing animal from Vegetable fibers, the former being colored y ellow by it, the latter remaining unchanged. It is employed in the laboratory to distinguish salts of potassium from those of sodium : the picrate of potassium being very sparingly soluble in water, while the picrate of sodium dissolves readily. Changing Clothing. Many persons lose life every year by an injudicious change of clothing, and the principles involved need repetition almost every year. If clothing is to be diminished, it should be done in the morning, when first dressing. Additional clothing may be put on at any time. In Northern States the under garments should not be changed for those less heavy sooner than the middle of May : for even in June a fire is very comfortable sometimes in a New York parlor. Woolen flannel ought to be worn next the person, by all, during the whole year, but a thinner material may tie worn after the first of June. A blazing fire should be kept in every family room until ten in the morning, and rekindled again an hour before sundown, up to the first week in June and from the first day of October. Particular and tidy housekeepers, by arranging their fireplaces for the summer too early, oftentimes put the whole family to a serious discomfort, and endanger health by exposing them to sit in chilliness for several hours every morning, waiting for the weather to moderate, rather than have the fireplace or grate all blackened up; that is, rather than be put to the trouble of another fixing up for the summer, they expose the children to croup and the old folks to inflammation of the lungs. The old and the young delight in warmth; it is to them the greatest luxury. Half the diseases of humanity would be swept from existence if the human body were kept comfortably warm all the time. The discomfort of cold feet, or of a chilly room, many have experienced to their sorrow; tlicy raaie the mind peevish and fretful while they expose the body to colds and inflammations which often destroy it in less than a week.—Halls Journal of Health.