Fig. 601.
Fig. 602.
Note.—Strangely, investigation has proved that water of this purity rapidly corrodes iron, and attacks even pure iron and steel more readily than “hard” water does, and sometimes gives a great deal of trouble where the metal is not homogeneous. Marine boilers would be rapidly ruined by pure distilled water if not previously “scaled” about 1⁄32 of an inch.
To deal properly with this subject the science of chemistry must be largely drawn upon; chemically pure water is that which has no impurities, and may be described as colorless, tasteless, without smell, transparent, and in a very slight degree compressible, and, were a quantity evaporated from a perfectly clean vessel, there would be no solid matter remaining. Now, in dealing with the impurities inside a boiler, it is to be observed that in no sense do they change the essential nature of water itself. The impurities are simply foreign bodies, which have no legitimate place in the boiler, and are to be expelled as thoroughly as possible.
The chemical substances to be eliminated are indicated in the note below. Water, on becoming steam, separates from the impurities which it may have contained, and these form sediment and incrustation. This is an important fact.
Corrosion is simply rusting or wasting away of the surfaces of the metals. Incrustation means simply a coating over.
Several approved recipes and “notes” of instruction for removing sediment and incrustation from steam boilers will be found near the close of this volume.
| Note.—Analysis of average boiler scale. Parts per 100 parts of deposit. | ||
|---|---|---|
| Silica | .042 | parts |
| Oxides of iron and aluminium | .044 | „ |
| Carbonate of lime | 30.780 | „ |
| Carbonate of magnesia | 51.733 | „ |
| Sulphate of soda | Trace | |
| Chloride of sodium | Trace | |
| Carbonate of soda | 9.341 | „ |
| Organic matter | 8.060 | „ |
| Total solids | 100. | parts |