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next into the front rank, the third covers him, and so on alternately in front and rear. The sergeant then divides the company into two platoons, of equal front, if possible; if the number of files is odd, the first platoon contains the even number. He then orders, "In each rank, count Twos." The two ranks count together. If the third file (whether complete, or a half-file) from the left counts "one," it is an odd file and has no number; the numbers of the two left files are then changed, so that the last file is "number two."

Each two files, or four men, Nos. "one" and "two," in the front and rear ranks, are called a group. The group never separates. It is for this reason that the first platoon must have an even number of files.

Every command in the squad-drill can be used for the company by substituting the word "company" for "squad." It only remains to state the differences occasioned by two ranks and the additional officers. In dressing, if the company is in line, the captain superintends the alignment from his place in line, or a corresponding place on the left; if in column, from a point two paces outside of the guide, upon whom the alignment is made, and facing toward that guide.

In facing to the right, the captain places himself on the left of the right guide, who always steps into the front rank before facing; in facing to the left, the captain is on the right of the left guide. After facing the rear rank, side-steps to the right or left, from the front rank; each rank then doubles, as if it were a squad. Thus, the company will be formed in a column of fours, touching elbows. Each group will be by itself, and there will be sufficient distance between the groups to avoid the lock-step. The fours will be formed as follows, ƒ denoting front rank, and r, rear :

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We will recapitulate those commands of the squad-drill which present any difference.

"By file right," or "left." Each group of four makes a wheel of the second variety, successively.

"Company ---- HALT ----FRONT" (when marching in fours, by the right or left flank). After undoubling, the rear rank closes up.

"Company, by the right flank." Files double, as in facing at a halt. "On the right, by file, into line." The captain and first sergeant commence the formation, followed by the front-rank men; the rear rank marks time at the word "MARCH," and does not commence the formation till four of the front rank are in line.

In a wheel by company from a halt, the right guide stands motionless until the word FRONT (the wheel being to the right); the man next him does not mark time, but faces at once to the right. The captain halts the company a little before the quarter-circle is completed; goes to the

point where the left will rest, and faces toward the man who has faced: the left guide steps up and touches the captain's breast with his left elbow; the captain places him exactly in line with the man on the right who faces, and orders, "Left ---- DRESS." A wheel to the left is precisely the converse.

To wheel by platoons, the order is, " By platoon, right wheel ---MARCH." The captain commands the first or right platoon, and the lientenant the second. The right guide of the company is the guide of the first platoon; the left guide of the company is the guide of the second platoon. The commander of each platoon dresses it to the left, the guide stepping out for that purpose, just as was explained for the captain in the last paragraph, the man on the right of each platoon facing to the right. After dressing, and ordering, "FRONT," each chief of platoon takes post two paces before the center of his command.

The column thus formed has its guides on the left, and is called a column "right in front." A column "left in front," formed by the command, "By platoon, left wheel---- MARCH," has its guides to the right. The platoon commanders and platoon guides are the same. At the command, "Guide right," given on the march, the guides change to that side.

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To march the column, the instructor orders, " Column forward, guide right [left] - - - - MARCH." To change the direction of the march, what is executed by a column of fours at the command, "By file right," or "left," he orders, "Head of column to the right." If the guides are not already on the left, he must first change them by the command, "Guide left," because in a wheel of the second kind the guide must be outward. The commander of the leaping platoon orders, "Right wheel ---- MARCH," “Forward - - - - MARCH;" the commander of the other platoon gives the same orders on arriving at the same place.

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The commands for halting and forming line are “ Column - - - - HALT,” 'Left into line wheel - - - - MARCH." The guides stand fast, the men next them face to the left; the chiefs of platoon halt their platoon; the captain dresses the whole company by the right, the lieutenant returning to his place at once; after the dressing, the instructor commands, " Guides POSTS," when the guides pass to their places.

A very showy movement is the one performed while on the march in fours by the command, "Open order ---- MARCH." The men of each group separate to two paces interval, instead of marching elbow to elbow. At the order, "Countermarch by file right--- MARCH," each of the four single files, in which the company is formed, countermarches separately. "Close order ---- MARCH," brings us back, closing in on the center. This is purely a show maneuver, not authorized by any system of tactics. The above movements will generally be found sufficient, if practiced until perfect accuracy is attained. Others may be taught from the ordinary books on tactics, if greater variety is desired.

THE

GLYCERINE AND NITRO-GLYCERINE.

HE late destructive explosions of nitro-glycerine in this city and in San Francisco, and the still more recent and appalling explosion at Aspinwall, have brought this compound into sudden and painful notoriety. Until these terrible disasters, which have followed each other in such quick succession, nitro-glycerine was comparatively unknown, except to chemists; and many who are familiar with glycerine and its use, especially in the toilet, are asking what is its composition, and how can a substance so simple and harmless be converted into one at once so powerful and dangerous?

GLYCERINE.

Glycerine is a nearly colorless, inodorous, intensely sweet, and very viscid liquid, nearly a third heavier than water. It is a compound of carbon, hydrogen, and oxygen, having the formula of (CH,O). It is soluble in all proportions in water and in alcohol, but nearly insoluble in ether. It can not be made to crystallize, and does not dry by exposure to the air. This latter property makes it exceedingly useful in medicine and the arts, and also for toilet purposes. It possesses remarkable antiseptic properties, and preserves animal tissues immersed in it in all their natural. colors. It may be distilled without decomposition in a current of superheated steam, at a temperature between 400° and 500°; but when exposed to dry heat, it is volatilized in part, while the remainder is decomposed, forming the pungent, tear-producing vapors called acrolein, so well known by those who live in the neighborhood of fat-boiling establishments.

When liquid oils are cooled to about 32°, or when solid fats are subjected to pressure between folds of bibulous paper, they are separated into two parts, one a liquid, and the other more or less concrete. The liquid is termed olein, and the solid, stearine, with which is associated a variable portion of margarine. Each of these is a compound of a distinct fatty acid, with the sweet principle glycerine, which constitutes about one-tenth part of all animal and vegetable oils. When fats and oils are decomposed by oxide of lead (litharge), the acids combine with the lead, forming the well-known lead plaster, and the glycerine is set free. It was in the manufacture of this article that glycerine was first discovered by Scheele, and for some time it was obtained entirely in this way. It is now produced in large quantity, and of perfect purity, in the manufacture of soap and candles. When fats are boiled with a strong solution of caustic potassa or soda, the alkali displaces the glycerine, and combines with the fatty acids, forming soap; the neutral fat, of whatever kind, being resolved into an alkaline salt of the fatty acids and into glycerine.

It is also obtained by the action of superheated steam on fat, a process lately introduced into the manufacture of candles. In this reaction, both the fatty acids and the glycerine assimilate the elements of water, and the excess of steam carries over a mechanical mixture of glycerine and fatty acids, which rapidly separates into two layers in the receiver.

NITRO-GLYCERINE.

When glycerine is added to equal parts of strong nitric and sulphuric acids, the heavy, oily-looking liquid nitro-glycerine is formed. It is sometimes called glonoine, and was shipped under this name on the illfated European. It is a substitution compound, in which two atoms of hydrogen of the glycerine are replaced by two of nitric acid. Its formula is therefore (C.H.(NO.),O.). Nitric acid alone decomposes glycerine, oxalic and carbonic acids being among the products.

Nitro-glycerine is a pale, yellow, oily liquid of 1.6 specific gravity, and insoluble in water. It is powerfully explosive and poisonous; a single drop placed upon the tongue will cause a violent headache, lasting for several hours. It explodes by percussion, or when confined and heated to about 360°. It does not explode by the mere application of fire. It was discovered in 1847, by M. Sorbrero, a pupil of M. Pelouze, who thought it too dangerous for practical use. Nothing was done with it until it was applied to blasting by a Swedish engineer, Mr. Alfred Noble, who claims to have so improved upon the original method of manufacturing the article, as to make it no more dangerous than gunpowder. But in view of the recent mysterious explosions, it would seem that his statements must be taken with considerable allowance. He has obtained a patent on his manufacture, which is commonly known by the name of Blasting Oil. According to Mr. Noble, this oil is composed of one part of glycerine and three parts of nitric acid, and can be kept an indefinite time without decomposition. It explodes with great rapidity, and with a force estimated to be thirteen times stronger than that of gunpowder. Consequently, smaller holes and fewer charges are required, and the miner's work is very much lessened. The oil is simply poured into the drill-holes, covered with water, and the charge fired by a waterproof fuse with a wellcharged percussion cap at the end. The explosion is so sudden that the water answers instead of tamping. It is sometimes poured through water into fissures, and fired in the same manner. It being insoluble, and heavier than water, it sinks to the bottom, and the water serves as a plug. It is, therefore, specially adapted to wet mining; and as the products of the combustion of blasting-oil are entirely gaseous, and not deleterious like those of gunpowder, it will doubtless supersede that article entirely for mining purposes, provided it can be made as safe to handle. For the present, however, too great care can not be taken in storing and transporting it.

JULIAN GURDON: SCHOOLMASTER.

CHAPTER X.

HAMERTON. THE EXPEDITION.

MY

Y first year at Hamerton Academy greatly tried my spirits, and tasked my powers. I had an exigent and fastidious public to satisfy. I had subordinate teachers, older and more experienced than myself, to conciliate and to harmonize among themselves; and I had pupils who had built much hope of lax rule and permitted deficiencies upon my quiet manners and apparent youth. But I was determined on success, and I gained it. At the close of the second term I was satisfied-every purpose I had sought was amply achieved.

In giving instruction, I had myself advanced in knowledge. My duties had not been arduous, and I had progressed in my favorite pursuits. Already I was quoted as an authority in natural science. My name was favorably known, even among European savans, and I was continually besought to contribute to the best periodicals upon my favorite topics. Hamerton was proud of me; Elmtown boasted that I had been nurtured at her bosom; and I by no means despised the more substantial rewards of my labors.

The long vacation which occurred at the close of my school year, I spent as I had the previous one, partly in a pedestrian tour, and partly in conference with persons interested, like myself, in scientific pursuits. Every step now was a step forward. I did not regret my return to my quiet avocation, because it left me ample time for the studies and experiments in which I was fast becoming an enthusiast; and I enjoyed it the more that I was initiating some of my pupils into these. studies, and that their ardor was to me a delightful stimulus.

The day came for the reopening of the school, and brought with it an unexpected pleasure-one of the keenest I ever experienced. All my pupils were gathered in the large hall appropriated to lectures and religious exercises. All rose as I entered, in greeting, and I bowed and glanced round to include all. To my surprise, my eye fell upon a familiar face-one I had scarcely expected to see again—that of Mary Lee.

She blushed and smiled as her eyes met mine. It was evident that our meeting was a mutual pleasure. The moment I was at liberty, I approached my dear pupil, and joyfully took her hand in mine. She was no longer a child; there was a slight reticence in her manner, but her gaze met mine with the old frankness and fearlessness. Pretty as a child, she had become a beautiful maiden. I had loved her before; I was charmed with her now. I learned that her father was absent in Europe; and that

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