White deposits

Because the thickness of the plate deposited from trivalent baths is limited, these have only been employed for decorative appHcations. However, the bluish white deposit obtained from chromic acid baths can be closely matched by trivalent chromium baths (173). 

Figure 8.3 General wastage of an aluminum water manifold from a diesel engine cooling system. Note the generally wasted internal surface due to concentrated caustic and the presence of white deposits and corrosion products.

Chromating Chromating is considered in Section IS.3. The chromate film on zinc is adherent and can be drab, yellow-green or colourless in appearance the colour varies considerably with the method of application. It retards white rust , the white deposit which sometimes forms on fresh zinc surfaces which are kept under humid conditions (see Section 4.7). A chromate film is damaged by heat and if used as a basis for paint adhesion, should preferably not be heated above 10°C, nor for longer than 1 h. 

Sulfates typically are found as a hard, dense, white deposit (occasionally in a thin, needle-like crystal form) of anhydrite (CaS04). 

Drusen Tiny yellow or white deposits in the retina. 

Ammonium thiocarbonate, (NH4)2CS3, may be prepared by digesting ammonium pentasulphide with carbon disulphide under a reflux condenser a white deposit of ammonium monosulphide first forms on the condensing surface and is gradually converted into the thiocarbonate, becoming pale oiange-coloured. On exposure to moist air it turns red. 

Air inlet louvers can sometimes be discolored by white deposits as a result of total evaporation of solids in cooling water partially wetting the louvers. 

Sulfates are typically found as hard, dense, white deposits, and often as thin needle-like crystals. Normally found in the highest heat-transfer areas. Sulfates do not dissolve when tested with concentrated HC1. 

Figure 11.32 Evaporating pure water leaves no deposit, while temporary or permanent hard water leaves white deposits behind.

When all of the air and moisture have been displaced from the tube, the selenium is strongly heated with a Bunsen flame. A white deposit of selenium dioxide forms on the surface of the selenium but as soon as the temperature has become high enough, it sublimes away. At the same time, the remaining selenium melts to a viscous mass and eventually burns with a pale-blue flame. The sublimate collects on the gas-delivery tube and on the sides of... 

Sulfide/hypo-alum toners are reusable and often improve with age. They usually contain a milky-white deposit, the result of sulfurization, which should not be filtered but stirred well before use. 

Platinum Plating.—A pure white deposit of platinum may be obtained by using a boiling solution consisting of ... 

A 59-year-old woman who for 20 years had taken chlorpromazine up to 1200 mg/day (mean dose 400 mg/day) gradually developed blurred vision in her left eye. Slit-lamp biomicroscopy showed multiple fine creamy-white deposits on her corneal endothelium and anterior crystalline lens capsule bilaterally. Microstructural analysis of the corneal endothelium showed that there were no abnormalities in cellular morphology resulting from these deposits. 

Examination shows a dusting of gray-white deposits in Bowman s layer or a slight hazing of the cornea early in the course of the disease. It typically starts at 3 and 9 o clock and progresses slowly toward the center, usually taking several months to years to coalesce and form a complete band across the interpalpebral cornea (Figure 26-13). The deposit is separated from the limbus by a clear zone and develops the characteristic Swiss cheese appearance because of the multiple clear areas within the plaque. 

In most cases, the deposition and polymerization proceed simultaneously, but under certain circumstances the delayed polymerization of the deposited monomer was observed. When a liquid nitrogen trap was used as the deposition surface, the polymerization of condensed monomer was observed when the temperature of the surface was allowed to rise. The conspicuous vigorous boiling of liquid nitrogen by the heat of polymerization, which caused abrupt change of white deposition to a clear film, was observed. 

The hydrate of formaldehyde, HOCH2OH, may under certain conditions polymerise in aqueous solution to form paraformaldehyde, H0CH2(0CH2) 0CH20H, which appears as a white deposit in the solution. The polymerisation may be prevented by adding to the solution 10-15% of methanol. 

Studies of the stability of the Li/MgO catalyst woe conducted by KExperiments performed ova a quartz diluted 3.1% Li/MgO catalyst showed a significant drop in methane convosion, but it did not change the catalyst selectivity. The lithium content in the post-reaction samples was detmnined to be around 0.1 wt%. A white deposit found downstream fron the reacts exit was identified as liOH. FurthernKxe, it was detemiined that lithium formed silicates with the quartz chips used as diluent and widi the quartz walls of the reactor. On the basis of these experimental results, Korf... 

Almost continuous daily exposure to aerosols, sufficient to leave a white deposit of DDT on nasal vibrissae of volunteers, produced moderate irritation of nose, throat, and eyes. Except for this irritation... 

For this, lower the bulb F, fill the cup a with coned H] 4 and open the 2-way cock c to admit the acid into E. Suck in some air by manipulating c right and left and then create some vacuum in E by closing c and leaving f open, while F remains si below E. Close f, remove E from the stand and shake it, while holding in two hands to wash the white deposit of mercuric sulfate from the walls. Replace E on the stand, raise F above E, open f, and, after the mixt has settled, let the acid and a few drops of mercury run through c and f, into a small beaker. Repeat the operation of cleaning once more and after the operations are completed, leave both capillaries in stopcock c and the capillary ij filled with mercury so as not to introduce any air in subsequent operations... 

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