Carbon Tetrachloride as a Cleaning and Solvent Agent
In recent years the use of carbon tetrachloride as a cleaning and solvent agent has considerably increased, owing partly to a decrease in its cost of production, and partly to a more widespread knowledge of its properties. The advantages which it possesses over naphtha in point of safety, with respect to both fire and explosion hazard, make this substance of considerable interest. Carbon tetrachloride is a water white liquid, having, when pure, a pleasant, agreeable odor quite similar to that of chloroform. The commercial product usually contains sulphur impurities which impart a slightly disagreeable odor. The specific gravity of the liquid at 32°F. is 1.632 and the boiling point is 169°F. The specific gravity of the vapor is about five and one-half times as great as that of air and about twice as great as that of the lightest naphthas. The difference in specific gravities of the vapors of carbon tetrachloride and naphtha is not sufficiently great, however, to overcome the tendency which all vapors have to diffuse, one within the other, and the two vapors do not separate once they have become thoroughly mixed. The two liquids show no tendency to separate once they have been mixed. Carbon tetrachloride is an excellent solvent of animal and vegetable fats, oils, varnishes, waxes, resins, mineral oils, paraffin, tar, etc. It is noninflammable and nonexplosive. Combustion cannot take place in its vapor due to the absence of oxygen. For this reason it extinguishes small fires in enclosed spaces, when thrown upon them.
The toxic properties of carbon tetrachloride are of importance where large quantities are used, and no provision is made for removing the vapors. Its effect on the human system is the same as that of chloroform, producing anesthesia, although not as powerful in its action. Until recently the cost of manufacture of carbon tetrachloride has been so great as to prohibit its general technical application, although for cleaning purposes, such as degreasing wool and removing oil and grease spots from finished cloth, it is fully as efficient as naphtha. Owing to this property, it is being used in a large number of patented preparations intended for use as cleaning agents, and is being sold under a variety of special trade names. These preparations sometimes contain other substances besides carbon tetrachloride, but they generally possess little or no advantage over the latter. On account of its non-inflammability and the property of smothering small fires when thrown upon them, carbon tetrachloride is being sold to-day as a fire extinguishing agent. In this role it has, however, disadvantages, owing to the liberation of large quantities of suffocating and poisonous gases, and the necessity of confining the vapor to the immediate seat of the fire. In spite of the fact that there have recently been further reductions in the price of carbon tetrachloride, its high cost is still the one serious drawback to its more general application, but the many advantages which carbon tetrachloride possesses over naphtha in point of safety make its use very desirable wherever practicable. The cost can be considerably reduced in many instances by reclaiming the spent solvent by distillation and by taking advantage of the fact that a certain percentage of naphtha can be added without rendering the mixture inflammable.
The importance of this matter of noninflammable mixtures of carbon tetrachloride and naphtha led to a series of tests, undertaken with the object of determining how great a percentage of various gravities could be added and still leave the mixture reasonably free from fire and explosion hazard. The following conclusions were drawn directly. from these tests, the proportion referring to percentage by volume:
- The percentage of naphtha which can be safely added varies considerably with the gravity.
- 55° naphtha at ordinary room temperatures is practically free from explosion hazard, but in order to be reasonably safe from fire hazard it should contain at least 30 per cent, of carbon tetrachloride.
- 63° naphtha at ordinary room temperatures presents but slight explosion hazard, but in order to be reasonably safe from fire hazard it should contain at least 45 per cent, of carbon tetrachloride.
- 70° naphtha, in order to be safe from explosion hazard, should contain at least 50 per cent, of carbon tetrachloride, and to be reasonably safe from fire hazard should contain 60 per cent.
- 76° naphtha, to be safe from explosion hazard, should contain at least 60 per cent, of carbon tetrachloride, and to be reasonably safe from fire hazard should contain 70 per cent.
The expression “reasonably safe from fire hazard” is used advisedly, since the above mixtures, while possessing but little fire hazard in open containers, will burn if spread out over a considerable area, on any readily combustible material, such as cotton goods. The percentages of naphtha, stated in each case, are limiting ones, and good practice would call for an additional 5 per cent, of carbon tetrachloride in order to allow some factor of safety. If such mixtures were used the cost would not be prohibitive, especially if the solvent were recovered by distillation, where large quantities are needed, and what additional cost there might be over pure naphtha would be more than offset by the greater security to life and property. In cases where distillation is carried on, the operation should be conducted in a safe location, since under certain conditions during part of the distillation pure naphtha may be obtained as a distillate. Owing to the fact that the above mixtures of carbon tetrachloride and naphtha will burn if spread on readily combustible material, they cannot be considered entirely satisfactory substitutes for pure carbon tetrachloride, and their use is recommended only in cases where the pure solvent cannot be used.
Some special improvements in the way of fire protection will be made this year at the state fair grounds, Phoenix, Ariz. Every precaution will be taken to prevent a serious fire, since the greater portion of the buildings, including the great grandstand, are built of wood. Chiet Wright, with city officials, has been completing arrangements for maintaining a steamer and chemical wagon at the fair grounds through the week. Firemen will also be quartered at the grounds.
*Paper prepared by Associated Factory Mutual Fire Insurance Companies (member N. F. P. A.). Reprinted from the October Quarterly of the National Fire Protection Association.