There are some good urinometers sold, but the number is small, and often the best are so large that they are not adapted to the pocket, and often it is impossible, when they are most needed, to get enough urine to fill the jar, while their required temperature of 60° F. is difficult and troublesome to attain. But by far the largest number sold are grossly inaccurate, and almost impossible to manage within the narrow limits of their utility.

Their defects are numerous and very general, but the defect which chiefly invalidates them is the cylindrical shape of the air chamber as seen at Fig. 4 of the following illustrations. This shape in a cylindrical jar but little larger than the hydrometer gives a line of contact and cohesion between the instrument and the inside of the jar which is fatal to a free movement up and down in the liquid, and therefore a free and correct floating is nearly impossible. It is quite impracticable to keep the instrument in the centre of the liquid even for a moment or two until read, and the moment it touches the jar the reading is so liable to serious error that the instrument may become not simply useless, but hurtful through giving information that misleads. Beside this, the stem is usually too large to give a distinct reading scale. A proper shape for the air chamber is that of a double cone, base to base, as seen in Fig. 1. In this there is but a single point of contact with the side of the jar, and thus the friction and cohesion is limited to the minimum degree. The stem should be as small as possible to contain the paper scale, because upon this depends the width of the subdivisions of the scale and the distinctness of the reading. The scale should extend from 1.000 to 1.060, and should be so divided that each figured line should represent 010, and each subdivision 001, or a unit in the third decimal place. The scale is sometimes marked without the decimal point, as 1000,-1010, etc., and sometimes the unit figure, decimal point and first 0 are omitted, and the scale simply reads 0,-10,20,-30, etc., the subdivisions being always the same. These latter forms of scale are good enough and are easily understood, but they are not the best form, and are not accurate in expression, for it is a specific gravity instrument, and water being unity, the other divisions are decimal fractions of unity, and should be so expressed. The scale should indicate the temperature to which it is adjusted, and this temperature should not be 60° F. or 62° F., as is common, but should be 25° C. 77° F. This latter is a much more convenient temperature because it is nearer to that of the modern sick room, and because if below that it can always be attained by the warmth of

the hand on the outside of the jar in a minute or two. And if the temperature of the room in which the urine has been standing is within two or three degrees of that either way it is sufficiently near. The urinometer being adjusted to read 1,000 in water at 25° C.= 77° F., the reading will be one unit of the third decimal place, or one subdivision of the scale, too high for each 3° C. 5.4° F. above that figure. Therefore if the urine be measured just after it is voided, say at 37° C. 98.6° F., it will indicate just '004, or four subdivisions of the scale above the true s. g. This of course is the highest temperature at which urine could be measured, and if such urine should indicate a s. g. of 1.026, and the 004 be subtracted from it for excess of temperature above that of the scale, the true indication would be 1.022. If a specimen of urine was tried at 3° C. =5.4°F. above the scale temperature, that is, at 28° C. 82.4° F., then it would be 001, or one subdivision above the true indication, and so on. It will thus be seen that four subdivisions of the scale is the greatest possible error from excess of temperature that this scale admits, and that being within the limit of variation of normal urine (about 1.018 to 1.028) is not a very serious matter in a large proportion of the applications of the instrument. Hence it is one of the advantages of this scale temperature of 25° C. 77° F. as a standard, that in a very large number of the instances of the very useful though negative applications of the urinometer, a thermometer is not essential, and is only needed when some abnormality shows the necessity for closer observations.

The next modification that the writer has to suggest is perhaps a still more important one, because it renders the use of the instrument easier, with far less liability to error. This improvement is in the jar, and consists in indenting the sides of the jar, as represented in Fig. 1, and in cross section by Fig. 2. The jar is cylindrical, as in common urinometers, but has a foot for steadier standing. The glass of the cylinder is softened in the lamp, and while soft is indented so as to make a V-shaped projection inside the jar. These longitudinal grooves or indentations are repeated, so that there are four in all, and the effect is that the hydrometer cannot come to the sides of the jar at all, but must either float free in the centre or touch one, or at most two of the sharp edges of these indentations, as shown in the section, Fig. 2, and where it does touch, it can only be by a single point of contact between two convex surfaces, and thus the friction and cohesion will be reduced to a minimum. The jar, as seen at Fig. 1, is made by the lamp, and the flutes or grooves

only occupy the middle half of the cylinder, but if made in a mould the grooves would extend from the lip to the foot, and this would be better, as then the jar would require still less urine to fill it. This is an important consideration, because it sometimes happens that the urine is very scanty when it is most important to know its density or s. g. All the apparatus is shown of full size in the illustrations, and the jar holds about 45 c. c., or 1 fluidounces, and when the urine is above the normal density a fluidounce or 30 c. c. will fill the jar sufficiently to float the hydrometer. If the indentations extended from top to bottom, as they should, somewhat less urine could be used.

The reading of the indications on the stem is a matter of importance, and requires the personal observation of each individual, and each will fall into a habit of reading, that will be sufficient, if adhered to, as long as the instrument lasts, but a good habit of reading is as easily fallen into as a bad one. Many persons read the indications from below the surface of the liquid, but this is not a good habit for two principal reasons: First, all hydrometers are constructed to be read from above the surface, because they are often used with colored and opaque liquids, which prevent reading from below; and secondly, because the distortion by the liquid is not inconsiderable, and varies with the density of the liquid. Therefore the indications should be read from above the liquid, or at least from above as well as below. The first thing essential to a moderately close reading is to have the stem entirely clean, for if greasy or soiled by the sebaceous matters of the fingers from handling, the liquid will not touch the stem in the proper manner for reading. When clean, the liquid piles up against the stem, covering from two to three divisions of the scale, and the rise of the liquid from the general level of the surface up against the stem gets thinner as it rises higher, so that the absolute point or feather-edge to which it rises cannot be seen, but there is generally a spot or section of a line of reflected light from the concave surface of the liquid when the stratum gets very thin upon the stem, that is useful as the line of proper reading, and the subdivision of the scale, which is nearest to this point when the instrument has come to rest, is the proper one to read. But very often this spot of light cannot be seen, or is seen as a broad and illdefined reflection; then let the instrument be pushed down a little and set to vibrating up and down, and while it is thus moving let the line of liquid be observed against the moving stem. The horizontal line of the liquid does not move, but the stem does, and by

the time the latter comes to rest the subdivision of the scale nearest to it will be easily seen, and when seen a few times it will be easily recognized ever after. The arrow in the cut points as nearly to the reading line as the engraver could make it with the object standing before him. As the flutings in the jar keep the instrument from coming to the side, there is always plenty of time for deliberate observation, and each observer will soon form a habit of observation quite correct enough to be within the sphere of general errors of all such instruments.

=

A small thermometer, graduated from 20° C. 68° F. up to about 35° C. 95° F., is needed to increase the accuracy of the indications where this is desired, but when the urinometer is carried to the bedside, and frequently used there, merely as an approximative inquiry as to the general character of the urinary excretion, or when it is to be left with the nurse for consecutive observations which are to decide whether closer observations be desirable,—or, in other words, whenever the physician desires to know whether the urinary excretion does or does not vary beyond the normal range of say '006,-then the instrument, whose extreme variation by temperature of the liquid does not exceed '004, does not need a thermometer, and when not needed it is an unnecessary expense, and an unnecessary risk to the whole apparatus to carry it.

The apparatus is best carried in a common, round, pasteboard box, into which it fits closely, and which can be renewed at small cost as often as it is worn out. The box is about 4 inches long by 1 in diameter, and bears a label on which may be printed the standardfor temperature of liquids, and the error of the instrument to be alluded to farther on.

For the double purpose of carrying it more safely and of absorbing the moisture from it after it has been rinsed out each time, thus saving the box from this moisture, a piece of old, thin, soft muslin about eight inches square is placed over the box and pushed down into it by the jar as it is put up after use. When the jar is in place another piece of similar soft thin muslin about 6 inches square is put over the mouth of the jar, and the hydrometer pushes this down with it into the jar. The thermometer can then be slipped down beside this, in the folds of the muslin, and the whole is well and easily packed, so as to be rather difficult to break with any ordinary usage.

This should be an instrument of very moderate cost, because very perishable and often to be replaced, and if of moderate cost it will