When the instrument has been carefully graduated, and has been constructed by an expert, the accuracy of the first two decimals may be relied upon. With a little practice in estimating the last drop, we may, in trying to estimate the density of water, even reach a closer approximation. In order to measure the height of the drop accurately, one should read the maximum height to which the liquid rises between the fall of two drops at the moment when the last ones are falling, since at that moment, and only at that, can it be ascertained that the lower level of the bubble is plane. The error in such reading does not reach half a millimeter, and, as a suitable height of the apparatus permits of having columns that vary between 13 and 30 centimeters, an error of this kind is but 1-300. This is the limit of precision of the method.
The clamp might be advantageously replaced by a glass cock, or, better still, A might terminate in a rubber bulb; and a lateral tubulure might be fixed to the pipette, and be closed with a rubber stopper.
This little apparatus is more easily maneuvered than any of those that have hitherto been devised upon the same principle. It is capable also of replacing areometers in ordinary determinations, since it permits of correcting the error in capillarity that is neglected in instruments; and, moreover, one can, when he desires to, easily verify for himself the accuracy of the graduation.—La Nature.
USEFUL BAGS, AND HOW TO MAKE THEM.
By JOHN T. HUMPHREY.
Since the papers on "Boot and Shoemaking," in vol. i. of Amateur Work, illustrated, I think nothing relating to the leather trades has appeared in it; and as there must be many among the readers of this magazine who have a desire to dive deeper into the art of manipulating leather into the various articles of utility made from that material, I will endeavor in the series of articles of which this is the commencement to furnish them with the necessary instructions which will enable them to do for themselves many things which now are left undone, or else have to be conveyed miles to some town where the particular business, or something akin to it, is carried on. To the colonist and those who live in out-of-the-way districts, it must be a matter of great regret to observe articles of use, where the material is in good condition, rapidly becoming useless owing to the inability of the possessor to do the necessary repairs. Again, it may be that the article is completely worn out, and the old proverb that "a stitch in time saves nine," will not be advantageously applied if carried out. In that case a knowledge of making new what we require, whether in order to replace something already worn out or as an addition to our store, must prove beneficial to the thrifty amateur. My object in writing these articles is not to deprive the mechanic of any portion of his legitimate occupation, but to assist those who live at a distance too great to be able to employ him, and who necessarily prefer any makeshift to the inconvenience of sending miles, and being without for days, an article which might possibly be set right in an hour or two.
HOW TO MAKE BAGS.
The old-fashioned carpet bag (Fig. 1) is still unsurpassed by any, where rough wear is the principal thing to be studied. Such a bag, if constructed of good Brussels carpeting and unquestionable workmanship, will last a lifetime, provided always that a substantial frame is used.
