For determining the influence of the rate of air-movement on the rate of cooling of the wet bulb, several processes have been employed, both in the open air and in the house.

1. In the first place, choosing a day when the air was considered nearly calm, (i.e. moving so gently that only leaves with very flexible petioles were swayed by it,) the wet bulb was first suspended at rest in this gentle current (A); secondly, it was carried across it (B) at the rate of 2.75 miles an hour; thirdly, it was swung across it at the rate of 6-18 miles an hour (C). The effects are recorded in the table below.

Experiment of 22nd Aug. 1846. Temperature of air 75°, of evaporation 63° (d=12).

Reciprocals of these numbers, which represent the cooling powers of the air in the several conditions, appear below:

and are obviously not in simple proportion to the velocity of the air-movement in the several cases. If we suppose the so-called 'calm' air to move two miles an hour (which the movement of smoke at the time seemed to indicate), the velocities, obtained by calculating the diagonals of the air-movements combined with the thermometer-movements, would be as under :

approach nearly to the ratio of the cooling powers.

2. Experiments of this kind however being unsusceptible of much precision, recourse was had to railway movement in a 'calm' day. Temperature of air 70°, of evaporation 64° (d=6). Time of cooling 1°, at 3 inches from the carriage window, 14"; at 18 inches, 10"; at 24 inches, 9".

Again, on another occasion, temperature of air 69°5, of evaporation 64° (d=55). Time of cooling 1°, at 20 inches distance from the window, 10". In each of these cases the real velocity of the train was believed to be about 36 miles an hour.

These experiments are sufficiently in accordance with those already discussed to allow of our applying the formula C = √ √ to all; where T is

с

dT

the observed time of cooling 1° and C a constant peculiar to the instrument. By taking C 300, and employing this value for the several experiments, the estimated and calculated results appear thus:—

As all these experiments are complicated with the uncertain and variable influence of what is called 'calm' air, their accordance with one general formula appears quite nt as could be expected. The drag of air, which the unequal rates different distances from the carriage indicate,

may perhaps not be wholly eliminated at even 20 or 24 inches distance. Perhaps no better mode of experiment on this peculiar transportation of the atmosphere by railway trains could be devised than the trial of its cooling power. In the first of the above experiments the air-displacement appeared to be about 13 miles an hour at 3 inches from the carriage; about 24 miles at 18 inches, and 30 miles at 24 inches.

The result now arrived at must, however, be regarded as only a first approximation, and requires to be tested and corrected by more rigorous processes. For this purpose the cooling of the wet bulb has been observed when carried round by a lathe movement, and when subject to the vibrations of a pendulum. The results are yet incomplete, but may be offered for the consideration of the Association on a future occasion.

Report on the Crystalline Slags. By JOHN PERCY, M.D. We have pleasure in now presenting to the Association the results of our investigation of the crystalline slags. It is obvious that such an investigation must be limited by the opportunity of obtaining specimens, which require to be diligently sought for at the various metallurgical works; and that, consequently, it is impossible for us at present to offer anything like a complete report upon this interesting subject. We have however been fortunate in procuring already an extensive series of beautifully crystallized slags, several of which we have not yet had time to examine. We are especially indebted to Mr. John Dawes, of West Bromwich, and to Messrs. Blackwell and Twamley, of Dudley, for many valuable contributions. In the present Report we have confined our attention to the slags produced in the smelting and manufacture of iron. We shall adopt the following arrangement:

1. The crystallographic and mineralogical description by Professor Miller. 2. The analysis*.

3. Special remarks.

The first series is composed of six specimens. Nos. 1 and 2 were obtained from hot-blast furnaces in the vicinity of Dudley; Nos. 3 and 4 from Messrs. Blackwell's hot-blast furnaces at Russell's-hall, near Dudley; No. 4 from one of Mr. Philip Williams's cold-blast furnaces, at the Wednesbury Oak Works, near Tipton; No. 6 was brought by Mr. Samuel Blackwell from a hot-blast furnace named La Providence, at Marchienne, Charleroi, Belgium. No. 3 was produced when the furnace was considered to be working unsatisfactorily, from some interruption to the free course of the blast. The crystals of the slag No. 3 are square prisms, terminated by planes perpendicular to the axis of the prism. Many of the prisms have their angles truncated by planes, making equal angles with the adjacent faces of the prism.

specific gravity of slag specific gravity of water

=2.9242.

Hardness 6. At 19.1 The crystals of slag No. 4 are square prisms, having the angles truncated like No. 3.

Hardness 55. At 18°2 C

specific gravity of slag specific gravity of water

=2.9187.

* I am happy to state that I have had the assistance of my friend Mr. David Forbes, brother of Professor Edward Forbes. To the analyses made by myself I shall append my own initials, and to those made by Mr. Forbes the initials of that gentleman.

The crystals of No. 5 are square prisms, having the angles truncated like No. 3. Hardness = 5'7.

Analysis. The slags composing the first series were found to contain silica, alumina, lime, magnesia, protoxides of manganese and iron, potass in small quantity, and sulphur as sulphuret. Phosphoric acid was also found in some of them. They are readily decomposed by digestion with dilute hydrochloric acid. The following method of analysis was adopted.

Method of Analysis.-1. The fine powder obtained by trituration in an agate mortar was digested with dilute hydrochloric acid. The whole was evaporated to dryness. The dry mass was treated with hydrochloric acid, and left for a few hours. Nitric acid was added sometimes before and sometimes after evaporation to peroxidize the iron. The silica separated by filtration was washed with boiling water until nitrate of silver ceased to produce the slightest turbidity, dried, incinerated at a bright red heat, cooled under a glass shade containing sulphuric acid, and then weighed.

2. To the acid solution was added a slight excess of ammonia. Filtration was conducted as rapidly as possible, the funnel being covered with a glass plate.

S. The precipitate (2) was boiled with potass. The solution was treated with an excess of hydrochloric acid, and the alumina then precipitated by carbonate of ammonia.

4. The insoluble residue (3) was dissolved in hydrochloric acid, and the iron was precipitated by succinate of soda or ammonia with the usual precautions.

5. The lime was precipitated by oxalate of ammonia from solution (2), after treatment by ammonia. The precipitate, which consisted of oxalate of lime mixed with oxalate of manganese, was incinerated at a bright red heat, and then digested with dilute acetic acid, which dissolved the lime and left the brown oxide of manganese. A slight excess of sulphuric acid was added to the solution of acetate of lime; the whole was evaporated to dryness, and heated to redness; from the sulphate of lime thus obtained the lime was calculated.

6. The solution (4), after separation of the iron, was added to solution (5) after separation of the lime. The manganese was precipitated by hydrosulphate of ammonia in a close vessel, and in every instance at least twelve hours were allowed for precipitation. The sulphuret of manganese was dissolved in hydrochloric acid, and precipitated as carbonate by carbonate of potass. The carbonate of manganese was incinerated at a bright red heat for a considerable time. The oxide of manganese thus produced was estimated as MnO+Mn2 O3.

7. The solution (6), after precipitation of the manganese, was digested with excess of hydrochloric acid until the sulphur separated by decomposition of the excess of hydrosulphate of ammonia had completely separated. The magnesia was precipitated by phosphate of soda and excess of ammonia. Generally twenty-four or forty hours were allowed for complete precipitation. The precipitate was washed with ammonia-water until no sensible residue was left by evaporat a plate of glass. When dry, generally as much of the magnesio ble was detached from the filter, and

slowly heated to redness; the filter, with what adhered to it, was then introduced into the crucible and incinerated as usual.

8. To determine the potass, the slag was digested as usual in hydrochloric acid, the iron was peroxidized by nitric acid, and the solution was then treated with excess of carbonate of ammonia. The filtrate was evaporated to dryness, and the ammoniacal salts were expelled by heat. The residue was treated with boiling water, and the solution filtered from the brownish residue. The filtrate was evaporated to dryness after the addition of excess of sulphuric acid. The residue was dissolved in water, acetate of baryta was added in excess, the sulphate of baryta was separated with the usual precautions by filtration; the filtrate was evaporated to dryness, and afterwards heated to redness. The solution contained the potass as carbonate; hydrochloric acid was added, and from the amount of chloride obtained by evaporation and heating to low redness, the potass was estimated. Berzelius's method of separating potass from magnesia by oxide of mercury was also occasionally resorted to.

9. The sulphur was determined either by oxidizing with strong nitrous acid, or by fusing with nitrate of potass and a mixture of carbonate of potass and soda. Chloride of barium was added to the acid solution. From the sulphate of baryta produced the sulphur was estimated.

10. The method resorted to for the detection of phosphoric acid will be described in each case.

The actual quantities of the substances found by analysis will always be given, in order that the calculations may be corrected in the event of any errors in the received atomic weights being corrected by future observers. The calculations have been made from the tables in the French translation of Rose's work by Peligot (Paris, 1843).

1. ANALYSIS. By J. P.

1. Weight of slag employed 27.57 grains, after having been gently heated over a spirit-lamp.

2. Silica 10-49.

3. Alumina 3.89.

4. Sulphate of lime 24.35.

5. Phosphate of magnesia (2MgO, P2 O3) 5.74.

6. Oxide of manganese (MnO+MnO2 O) 0-12.

7. Sesquioxide of iron 0.39.

S. Potass. Weight of slag employed 50-47 grains. Chloride of potassium 1.48. A minute quantity of precipitate was produced by the addition of antimoniate of potass to the solution. The quantity of chlorine was determined by nitrate of silver. The chloride of silver obtained weighed 2.814 grains, which correspond to 0.694 of chlorine. 148 of chloride of potassium by the tables, contains 0·702 of chlorine. Difference 0·702-0·694=0·008. The chloride may therefore be estimated as nearly pure chloride of potassium. 9. Sulphur. Hydrosulphuric acid was liberated by the action of hydrochloric acid. Weight of slag 22.68. The nitrous acid process was employed. The sulphate of baryta weighed 0.59. It was ascertained that the slag did not contain sulphuric acid. The sulphur is admitted to exist as sulphuret of calcium.

10. Phosphoric acid was not detected. Weight of the slag employed 51.38 grains. It was digested with hydrochloric acid, and the silica separated as usual. The precipitate obtained by the addition of ammonia in slight excess was dissolved by hydrochloric acid; tartaric acid was added,

and then chloride of magnesium and excess of ammonia; no trace of the characteristic precipitate of phosphate of magnesia and ammonia appeared after several days.

1. Weight of slag employed 25-41 grains, after having been gently heated over a spirit-lamp; the odour of free sulphur was distinctly remarked. 2. Silica 9.85

3. Alumina 3.68.

4. Sulphate of lime 22.04.

5. Phosphate of magnesia 4.76.

6. Oxide of manganese 007.

7. Sesquioxide of iron 0.34.

8. Potass. Weight of slag employed 46.93. Chloride of potassium 0.82. By treatment with nitrate of silver 1.51 grain of chloride of silver was obtained, which corresponds to 0.372 of chlorine. O'82 of chloride of potassium contains 0.389 of chlorine.

9. Sulphur. Hydrosulphuric acid was evolved by the action of hydrochloric acid. Weight of slag 2006. The nitrous acid process was employed. The sulphate of baryta weighed 0.63.

10. Phosphoric acid was not sought for.

1. Weight of the slag employed 25-27, after having been gently heated

over a spirit-lamp.

2. Silica 9.51.

3. Alumina 3.23.

4. Sulphate of lime 20.68.

5. Phosphate of magnesia 4.58.

6. Oxide of manganese 0.72.

7. Sesquioxide of iron 1.18.