It may often be of interest to know what part of the loss, on ignition, is due to water in form of moisture. In such cases the sample should first be dried to constant weight in a steam-bath and then ignited. In the following data are found the results obtained here with samples treated as above indicated and also ignited directly. Number one is a basic slag two years old and the others Florida phosphates.
| Heated to 100° C. then ignited. | Ignited directly. | ||||
|---|---|---|---|---|---|
| Loss at 100° C. | Loss on ignition. | Total loss. | Loss on ignition. | ||
| No. 1 | (Slag) | 2.57 | 1.77 | 4.34 | 4.12 |
| No. 2 | (Rock) | 2.61 | 5.19 | 7.80 | 8.06 |
| No. 3 | “ | 1.09 | 5.77 | 6.86 | 6.90 |
| No. 4 | “ | 0.42 | 9.20 | 9.62 | 9.58 |
| No. 5 | “ | 1.81 | 4.83 | 6.64 | 6.40 |
| No. 6 | “ | 4.36 | 6.52 | 10.88 | 10.83 |
| No. 7 | “ | 3.31 | 7.01 | 10.32 | 10.67 |
(6) Presence of Sulfids.—Another point noticed in this laboratory is that the basic slags uniformly contain sulfids which are decomposed upon the addition of an acid with an evolution of hydrogen sulfid.
(7) Presence of Fluorin.—In applying the test for fluorin, it has been uniformly found here that the mineral phosphates respond to the fluorin test while the basic slags, on the contrary, respond to the hydrogen sulfid test. This test, however, was applied only to the few samples we have had and may not be a uniform property.
The absence of fluorin might not prove the absence of adulteration, but its presence would, I believe, certainly prove the fact of the adulteration in that particular sample.
The fluorin test is applied by Böttcher in the following manner:[76] From ten to fifteen grams of the slag are placed in a beaker ten centimeters high and from five to six centimeters in diameter, with fifteen cubic centimeters of concentrated sulfuric acid, stirred with a glass rod, and covered with a watch-glass on the under side of which a drop of water hangs. If there be formed upon the drop of water a white murky rim, it is proof that a mineral phosphate containing fluorin has been added. After from five to ten minutes you can notice on the clean watch-glass the etching produced by the hydrofluoric acid. According to Böttcher an adulteration of ten per cent of raw phosphate in slag can be detected by this method.
(8) Solubility in Water.—Solubility in water is also a good indication, natural phosphates being totally insoluble in water, while a considerable quantity of the basic slag will be dissolved in water on account of the calcium oxid or hydroxid which it contains. If the loss on ignition is low, and the volume-weight and water-solubility high, the analyst may be certain that the sample is a pure slag.
In comparative tests made in our laboratory with a sample of basic slag and seven samples of Florida phosphate, the percentages of material dissolved by water and by a five per cent solution of citric acid were found to be as follows:
| Water-soluble. Per cent. | Sol. in five per cent citric acid. Per cent. | ||
|---|---|---|---|
| Odorless | phosphate | 0.97 | 16.10 |
| Florida | phosphate | 0.01 | 4.15 |
| “ | “ | 0.09 | 4.66 |
| “ | “ | 0.02 | 3.43 |
| “ | “ | 0.08 | 3.61 |
| “ | “ | 0.02 | 3.79 |
| “ | “ | 0.05 | 4.46 |
| “ | “ | 0.02 | 4.24 |
From the above data it is seen that the solvent action of water especially would be of value inasmuch as it dissolves only a mere trace of the mineral phosphates, approximating one per cent of the amount dissolved from basic slag. In the case of the citric acid it is found that the amount of materials soluble in this solvent for basic slag is fully four times as great as for the mineral phosphates. Both of these processes, therefore, have considerable value for discriminating between the pure and adulterated article of basic slag.